Non-aqueous electrolyte solution

ABSTRACT

To provide a non-aqueous electrolyte solution, a non-aqueous secondary battery, a cell pack, and a hybrid power system, capable of improving desired battery performance in an acetonitrile electrolyte solution, the non-aqueous electrolyte solution contains a non-aqueous solvent, PO 2 F 2  anions, and cyclic acid anhydride.

FIELD OF THE INVENTION

The present invention relates to a non-aqueous electrolyte solution, anon-aqueous secondary battery, a cell pack, and a hybrid power system.

BACKGROUND OF THE INVENTION

A non-aqueous secondary battery such as a lithium ion battery (LIB) ischaracterized in a light weight, high energy, and a long service life,and is widely used as a power source of various portable electronicdevices. In recent years, applications of the non-aqueous secondarybatteries are widened to an industrial field represented by a power toolsuch as an electric tool, an in-vehicle device in an electric bicycle,or the like. Furthermore, attention is also focused in the field of apower storage field such as a home energy storage system.

Patent Document 1 discusses a non-aqueous electrolyte solution of alithium ion battery. In the technique of Patent Document 1, durabilityis evaluation by measuring a capacity after a predetermined cyclethrough a high-temperature cycle test or the like.

Patent Document 2 discusses a non-aqueous electrolyte solution for alithium secondary battery, capable of improving an initial capacity andan output power characteristic at a room temperature and a lowtemperature. In the technique of Patent Document 2, the non-aqueouselectrolyte solution contains an organic solvent, lithium salt, and aphosphorus compound.

Patent Document 3 discusses a battery technique capable of improving aservice life and a rate characteristic by modifying a positive electrodematerial of the secondary battery.

CITATION LIST Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Application    Publication No. 2014-194930-   Patent Document 2: Japanese Translation of PCT International    Application Publication No. 2016-531388-   Patent Document 3: Japanese Unexamined Patent Application    Publication No. 10-208742

SUMMARY OF THE INVENTION

However, it is known that an acetonitrile-based electrolyte solution isrequired to form a film on a surface of a negative electrode in order tosuppress reductive electrolysis, and a film formation agent used in theprior art is insufficient.

From the discussion described above, it is known that, if a film thatcan withstand the acetonitrile electrolyte solution is not sufficientlyformed, reductive decomposition proceeds at the time of initial chargingor each test under a high-temperature environment to cause gasgeneration, capacity reduction, or the like.

Meanwhile, if a highly durable film is formed, insertion or dissociationof lithium ions to or from the negative electrode is inhibited, so thatit is difficult to exhibit high ion conductivity which is thecharacteristic of the acetonitrile.

In this regard, in order to address the problems of the prior art, thepresent invention provides a non-aqueous electrolyte solution, anon-aqueous secondary battery, a cell pack, and a hybrid power system,particularly, capable of improving desired battery performance in anacetonitrile electrolyte solution.

According to the present invention, there is provided a non-aqueouselectrolyte solution containing a non-aqueous solvent, PO₂F₂ anions, andcyclic acid anhydride.

In the present invention, it is preferable that a content of the PO₂F₂anions is 0.001 mass % or more and 1 mass % or less with respect to thenon-aqueous electrolyte solution.

In the present invention, it is preferable that the PO₂F₂ anions areobtained by dissociating LiPO₂F₂.

In the present invention, it is preferable that the cyclic acidanhydride includes at least one of succinic anhydride, maleic anhydride,and phthalic anhydride.

In the present invention, it is preferable that the cyclic acidanhydride includes at least succinic anhydride.

In the present invention, it is preferable that a content of the cyclicacid anhydride is 0.01 mass % or more and 1 mass % or less with respectto the non-aqueous electrolyte solution.

In the present invention, it is preferable that the non-aqueous solventcontains at least acetonitrile.

In the present invention, it is preferable that the non-aqueouselectrolyte solution further contains PF₆ anions.

In the present invention, it is preferable that the PF₆ anions areobtained by dissociating LiPF₆.

In the present invention, it is preferable that the non-aqueouselectrolyte solution further contains linear carbonate.

In the present invention, it is preferable that the linear carbonate isat least one selected from a group consisting of diethyl carbonate,ethyl methyl carbonate, and dimethyl carbonate.

In the present invention, it is preferable that the non-aqueous solventcontains acetonitrile, and a molar mixing ratio of the linear carbonaterelative to the acetonitrile is 0.15 or higher and 2 or lower.

In the present invention, it is preferable that the non-aqueous solventcontains acetonitrile, and a molar mixing ratio of the linear carbonaterelative to the acetonitrile is 0.25 or higher and 2 or lower.

In the present invention, it is preferable that the non-aqueous solventcontains acetonitrile, and a molar mixing ratio of the linear carbonaterelative to the acetonitrile is 0.4 or higher and 2 or lower.

In the present invention, it is preferable that the non-aqueouselectrolyte solution further contains imide salt.

In the present invention, it is preferable that the imide salt includesat least one selected from a group consisting of LiN(SO₂F)₂ andLiN(SO₂CF₃)₂.

In the present invention, it is preferable that a main component of thelithium salt is the imide salt, or the imide salt and the lithium saltother than the imide salt are contained as the main component in thesame amount.

In the present invention, it is preferable that the imide salt iscontained in a molarity relationship of “LiPF₆ imide salt”.

In the present invention, it is preferable that a content of the imidesalt is 0.5 mol or more and 3.0 mol or less with respect to anon-aqueous solvent of 1 L.

In the present invention, it is preferable that the non-aqueous solventcontains acetonitrile, and a molar mixing ratio of PF₆ anions relativeto the acetonitrile is 0.01 or higher and lower than 0.08.

In the present invention, it is preferable that the non-aqueouselectrolyte solution further contains cyclic carbonate without saturatedsecondary carbon.

In the present invention, it is preferable that the cyclic carbonatewithout saturated secondary carbon includes at least one selected from agroup consisting of ethylene carbonate and vinylene carbonate.

In the present invention, it is preferable that the cyclic carbonatewithout saturated secondary carbon is vinylene carbonate, and a contentof vinylene carbonate of 4 volume % or less is contained in thenon-aqueous electrolyte solution.

In the present invention, it is preferable that a −30° C. ionicconductivity of the non-aqueous electrolyte solution is 3 mS/cm orhigher.

In the present invention, it is preferable that a 0° C. ionicconductivity of the non-aqueous electrolyte solution is 10 mS/cm orhigher.

In the present invention, it is preferable that a 20° C. ionicconductivity of the non-aqueous electrolyte solution is 15 mS/cm orhigher.

According to the present invention, there is provided a non-aqueouselectrolyte solution containing a non-aqueous solvent and lithium salt,wherein activation energy in ion conduction is 15 kJ/mol or lower at atemperature of −20 to 0° C.

In the present invention, it is preferable that activation energy in theion conduction is 15 kJ/mol or lower at a temperature of 0 to 20° C.

In the present invention, it is preferable that the non-aqueouselectrolyte solution further contains a compound expressed as thefollowing Formula (1).[Chemical Formula 1]—N═  Formula (1)

In the present invention, it is preferable that the compound is anitrogen-containing cyclic compound.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and a non-aqueous electrolyte solution,wherein the non-aqueous electrolyte solution contains acetonitrile andLiPO₂F₂, and a value obtained by dividing a bulk resistance at atemperature of −30° C. by an internal resistance value in measurement ofelectrochemical impedance spectroscopy for the non-aqueous secondarybattery is 0.05 to 0.7.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains a compound having at least one functional group selected from agroup consisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—, and a valueobtained by dividing a bulk resistance at a temperature of −30° C. by aninternal resistance value in measurement of electrochemical impedancespectroscopy for the non-aqueous secondary battery is 0.05 to 0.7.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and a non-aqueous electrolyte solution,wherein the negative-electrode active material layer contains at leastone compound selected from a group consisting of imide salt and (SO₄)²⁻,the imide salt is at least one selected from a group consisting oflithium salt and onium salt, and a bulk resistance at a temperature of25° C. in measurement of electrochemical impedance spectroscopy for thenon-aqueous secondary battery is 0.025 ohm or smaller.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains at least one compound selected from a group consisting oforganic acid, salt thereof, acid anhydride, and Li₂O, the organic acidincludes at least one of acetic acid, oxalic acid, and formic acid, anda value obtained by dividing a bulk resistance at a temperature of −30°C. by an internal resistance value in measurement of electrochemicalimpedance spectroscopy for the non-aqueous secondary battery is 0.05 to0.7.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and a non-aqueous electrolyte solution,wherein the negative-electrode active material layer contains at leastone compound selected from a group consisting of imide salt and (SO₄)²⁻,the imide salt is at least one selected from a group consisting oflithium salt and onium salt, and a bulk resistance at a temperature of−30° C. in measurement of electrochemical impedance spectroscopy for thenon-aqueous secondary battery is 0.07 ohm or smaller.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains a compound having at least one functional group selected from agroup consisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—, and thenon-aqueous secondary battery has a capacity retention rate of 70% orhigher, the capacity retention rate being calculated by dividing a 5 Cdischarge capacity by a 1 C discharge capacity after a storage test for4 hours at 85° C.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains at least one compound selected from a group consisting oforganic acid, salt thereof, acid anhydride, and Li₂O, the organic acidincludes at least one acetic acid, oxalic acid, and formic acid, and thenon-aqueous secondary battery has a capacity retention rate of 70% orhigher, the capacity retention rate being calculated by dividing a 5 Cdischarge capacity by a 1 C discharge capacity after a storage test for4 hours at 85° C.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains a compound having at least one functional group selected from agroup consisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—, and thenon-aqueous secondary battery has a 0° C. ionic conductivity of 10 mS/cmor higher after a storage test for 4 hours at 85° C.

According to the present invention, there is provided a non-aqueoussecondary battery including: a positive electrode having apositive-electrode active material layer formed on one surface or bothsurfaces of a current collector; a negative electrode having anegative-electrode active material layer formed on one surface or bothsurfaces of a current collector; and the non-aqueous electrolytesolution described above, wherein the non-aqueous secondary batterycontains at least one compound selected from a group consisting oforganic acid, salt thereof, acid anhydride, and Li₂O, the organic acidincludes at least one of acetic acid, oxalic acid, and formic acid, andthe non-aqueous secondary battery has a 0° C. ionic conductivity of 10mS/cm or higher after a storage test for 4 hours at 85° C.

In the present invention, it is preferable that the positive-electrodeactive material is a lithium-containing composite metal oxide expressedas “Li_(z)MO₂” (where “M” contains Ni and one or more metal elementsselected from a group consisting of Mn, Co, Al, and Mg, a content ratioof the Ni element is more than 50%, and “z” denotes a number greaterthan 0.9 and smaller than 1.2).

In the present invention, it is preferable that a difference of thenegative electrode electric potential around injection of thenon-aqueous electrolyte solution is 0.3 V or higher.

In the present invention, it is preferable that a gas generation amountin a storage test at 60° C. for 200 hours is 0.008 ml or less per 1 mAh.

In the present invention, it is preferable that a resistance increaserate in a full-charge storage test at 60° C. for 720 hours is 400% orlower.

According to the present invention, there is provided a cell packcomprising the non-aqueous secondary battery described above, whereinthe positive-electrode active material layer contains alithium-containing compound including Fe, the negative-electrode activematerial layer contains graphite or at least one or more elementsselected from a group consisting of Ti, V, Sn, Cr, Mn, Fe, Co, Ni, Zn,Al, Si, and B, the non-aqueous electrolyte solution contains cycliccarbonate without saturated secondary carbon, the cyclic carbonatewithout saturated secondary carbon is at least one selected from a groupconsisting of ethylene carbonate and vinylene carbonate, the non-aqueoussecondary battery is configured by connecting one module or two or moremodules, in which the module is obtained by connecting four cells inseries, in parallel or the non-aqueous secondary battery is configuredby connecting four modules, in which the module is obtained byconnecting two or more cells in parallel, in series, an operationvoltage range per cell is within a range of 1.8 to 3.7 V, an averageoperation voltage is 2.5 to 3.5 V, and the module is mounted with abattery management system (BMS).

According to the present invention, there is provided a hybrid powersystem obtained by combining the cell pack described above, and a moduleor cell pack having a secondary battery other than a lithium ionbattery.

According to the present invention, there is provided a cell packcomprising the non-aqueous secondary battery described above, whereinthe positive-electrode active material layer contains alithium-containing compound including Fe, the negative-electrode activematerial layer contains graphite or at least one or more elementsselected from a group consisting of Ti, V, Sn, Cr, Mn, Fe, Co, Ni, Zn,Al, Si, and B, the non-aqueous electrolyte solution contains cycliccarbonate without saturated secondary carbon, the cyclic carbonatewithout saturated secondary carbon is at least one selected from a groupconsisting of ethylene carbonate and vinylene carbonate, the cell packis configured by connecting one cell pack or two or more cell packs inparallel on the basis of Formula (2) and Formula (3), in which thenumber of cells and the number of modules of the non-aqueous secondarybattery are defined, or the non-aqueous secondary battery is configuredby connecting modules on the basis of Formula (2) and Formula (3), themodule being obtained by connecting two or more cells in parallel, anoperation voltage range per cell is within a range of 1.8 to 3.7 V, anaverage operation voltage is 2.5 to 3.5 V, and the module is mountedwith a battery management system (BMS).Number of cells connected in series per module (X): X=2,4,8, or16  Formula (2):Number of modules connected in series per cell pack (Y):Y=16/X.  Formula (3):

According to the present invention, there is provided a hybrid powersystem including the cell pack described above, and a module or cellpack having a secondary battery other than a lithium ion battery incombination.

Using the non-aqueous electrolyte solution according to the presentinvention, it is possible to delay generation of gas in the event ofhigh-temperature operation and overcharging, reinforce the negativeelectrode SEI, and obtain excellent low-temperature characteristics oroutput power characteristics and excellent high-temperaturecharacteristics.

As described above, using the non-aqueous electrolyte solution and thenon-aqueous secondary battery using the same according to the presentinvention, it is possible to provide an acetonitrile electrolytesolution capable of improving desired battery performance.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view schematically illustrating an exemplarynon-aqueous secondary battery according to an embodiment of theinvention;

FIG. 2 is a cross-sectional view taken along the line A-A of thenon-aqueous secondary battery of FIG. 1;

FIGS. 3(a) and (b) are a schematic explanatory diagram illustrating acell pack according to a forty fourth embodiment;

FIG. 4 is a schematic explanatory diagram illustrating a hybrid powersystem according to a forty fifth embodiment;

FIG. 5 is a schematic explanatory diagram illustrating a cell packaccording to a forty sixth embodiment; and

FIG. 6 is a schematic explanatory diagram illustrating a hybrid powersystem according to forty seventh embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention (hereinafter, simply referred to as“embodiment”) will now be described in details.

First Embodiment: Non-Aqueous Electrolyte Solution

First, a technical change at the time of development of the presentinvention will be described. Acetonitrile has a high potential as asolvent of the electrolyte solution due to excellent balance betweenviscosity and relative dielectric constant. For this reason, anelectrolyte solution for a lithium ion battery provided withacetonitrile as a non-aqueous solvent has an excellent low-temperaturecharacteristic. However, since acetonitrile has low resistance toreduction, there has been a problem that, when a reduction reaction siteof the negative electrode is activated at a high temperature in the caseof a lithium ion battery, the reductive decomposition of acetonitrilerapidly proceeds. For this reason, when the lithium ion battery isstored at a high temperature, reduction of acetonitrile is promoted, andgas is generated to cause battery swelling disadvantageously. In thisregard, the inventors have developed the invention for suppressingbattery swelling when the lithium ion battery using the electrolytesolution is at a high temperature by appropriately adjusting the typeand the content of the additives to be added in the non-aqueouselectrolyte solution, particularly an electrolyte solution containingacetonitrile. That is, this embodiment includes the followingcharacteristic parts.

A non-aqueous electrolyte solution according to a first embodimentcontains a non-aqueous solvent, PO₂F₂ anions, and cyclic acid anhydride.

In this manner, the non-aqueous electrolyte solution according to thefirst embodiment contains PO₂F₂ anions and cyclic acid anhydride inaddition to the non-aqueous solvent.

The PO₂F₂ anions and the cyclic acid anhydride form a robust passivefilm called a solid electrolyte interface (SEI) on the negativeelectrode when an electrolyte solution containing them is used in thenon-aqueous secondary battery. Although the SEI has ion conductivity, itdoes not have electron conductivity, so that reductive decomposition ofthe electrolyte solution is suppressed. Due to the PO₂F₂ anions and thecyclic acid anhydride, the SEI formed on the negative electrode isreinforced, so that the reductive decomposition of the electrolytesolution is effectively suppressed. As a result, when the non-aqueoussecondary battery is heated to a high temperature, a reduction reactionof the electrolyte solution is promoted, and generation of gas issuppressed, so that battery swelling is suppressed.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to this embodiment can suppress reductivedecomposition of the non-aqueous electrolyte solution in the event ofhigh-temperature heating and suppress battery swelling at a hightemperature.

For this reason, the non-aqueous secondary battery according to thisembodiment can be applied to a high-temperature region, for example, ata temperature of 60° C. and is applicable to, for example, outdoorapplications in summer or the like.

The non-aqueous secondary battery according to this embodiment has apositive electrode having a positive-electrode active material layerformed on one surface or both surfaces of a current collector, anegative electrode having a negative-electrode active material layerformed on one surface or both surfaces of a current collector, and anon-aqueous electrolyte solution.

The non-aqueous electrolyte solution contains, for example, anon-aqueous solvent, lithium salt, PO₂F₂ anions, and at least oneselected from a group consisting of succinic anhydride (SAH), maleicanhydride (MAH), and phthalic anhydride (PAH) as the cyclic acidanhydride. Specifically, the non-aqueous electrolyte solution contains,for example, acetonitrile, imide salt such as LiPF₆, LiN(SO₂F)₂ orLiN(SO₂CF₃)₂, SAH, and LiPO₂F₂. In this case, in the non-aqueoussecondary battery, there is no particular limitation in the negativeelectrode, the positive electrode, the separator, and the batterycasing.

The configuration described above has a remarkable effect of suppressingan increase of resistance during high-temperature heating and obtaininglow-temperature characteristics.

Second Embodiment: Non-Aqueous Electrolyte Solution

According to the second embodiment, in the non-aqueous electrolytesolution of the first embodiment, the content of PO₂F₂ anions preferablyhas a range of 0.001 mass % or more and 1 mass % or less with respect tothe non-aqueous electrolyte solution.

The non-aqueous electrolyte solution according to the second embodimentpreferably contains acetonitrile, PF₆ anions, PO₂F₂ anions, cyclic acidanhydride, and imide salt. Among them, the PO₂F₂ anions and the cyclicacid anhydride contribute to suppression of an increase of internalresistance during high-temperature heating. In addition, the imide saltcontributes to improvement of the low-temperature characteristics. Here,the imide salt refers to lithium salt expressed as expressed as“LiN(SO₂C_(m)F_(2m+1))₂” (where “m” denotes an integer of 0 to 8).

Due to the composition of the non-aqueous electrolyte solution accordingto this embodiment, it is possible to suppress an increase of internalresistance during high-temperature heating and obtain excellentlow-temperature characteristics.

Note that the low-temperature characteristics can be determined on thebasis of the ionic conductivity at a low temperature (specifically, −10°C. or −30° C.).

According to the second embodiment, the content of PO₂F₂ anions has arange of 0.001 mass % or more and 1 mass % or less with respect to thenon-aqueous electrolyte solution. In addition, the content of cyclicacid anhydride preferably has a range of 0.01 mass % or more and 1 mass% or less with respect to the non-aqueous electrolyte solution.Furthermore, the non-aqueous electrolyte solution contains imide saltwith a molarity relationship of “LiPF₆≤imide salt”. Here, the contentsof PO₂F₂ anions and the cyclic acid anhydride are expressed as massratios by assuming that a sum of all components of the non-aqueouselectrolyte solution is set to 100 mass %. In addition, the molaritiesof LiPF₆ and imide salt are measured for the non-aqueous solvent of “1L”.

By defining the contents and the molarities as described above, PO₂F₂anions and cyclic acid anhydride form a robust SEI on the negativeelectrode. In this manner, since a passive film called “SEI” is formedon the negative electrode, it is possible to effectively suppress anincrease of resistance during high-temperature heating.

Since the imide salt is contained with a molarity relationship of“LiPF₆≤imide salt”, it is possible to suppress a decrease of the ionicconductivity at a low temperature and obtain excellent low-temperaturecharacteristics.

The content of PO₂F₂ anions is more preferably 0.05 mass % or more and 1mass % or less with respect to the non-aqueous electrolyte solution. Inaddition, the content of cyclic acid anhydride is more preferably 0.1mass % or more and 0.5 mass % or less with respect to the non-aqueouselectrolyte solution.

The content of imide salt is preferably 0.5 mol or more and 3 mol orless with respect to the non-aqueous solvent of “1 L”.

As a result, it is possible to more effectively suppress an increase ofresistance during high-temperature heating and obtain more excellentlow-temperature characteristics.

According to this embodiment, it is possible to suppress a resistanceincrease rate to 400% or lower in a full-charge storage test for 720hours at 60° C., but not limited thereto. In addition, preferably, it ispossible to suppress the resistance increase rate to 300% or lower. Morepreferably, it is possible to suppress the resistance increase rate to250% or lower.

According to this embodiment, the ionic conductivity at a temperature of−10° C. is preferably 10 mS/cm or higher, but not limited thereto. Morepreferably, the ionic conductivity at a temperature of −10° C. is 12mS/cm or higher, and furthermore preferably, 12.5 mS/cm or higher.

According to this embodiment, the ionic conductivity at a temperature of−30° C. is 3 mS/cm or higher, and more preferably, 5 mS/cm or higher,but not limited thereto. Furthermore preferably, the ionic conductivityat a temperature of −30° C. is 6 mS/cm or higher, and furthermorepreferably, the ionic conductivity at a temperature of −30° C. is 6.5mS/cm or higher.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to this embodiment may function as a battery throughinitial charging. However, a part of the electrolyte solution isdecomposed at the time of the initial charging for stabilization. Inthis case, since the content of PO₂F₂ anions or cyclic acid anhydride inthe electrolyte solution is originally small, and they are incorporatedinto the SEI, or due to other reasons, it was difficult to detect acomponent after the initial charging in some cases.

For this reason, in the non-aqueous secondary battery using theLiPF₆-based acetonitrile electrolyte solution, if the aforementionedproperties are provided after the initial charging, it can be inferredthat the components of the non-aqueous electrolyte solution according tothis embodiment are contained.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the first and second embodiments may include apositive electrode, a negative electrode, and a non-aqueous electrolytesolution. In addition, the resistance increase rate may be 400% or lowerin a full-charge storage test for 720 hours at 60° C., and the ionicconductivity at −10° C. may be 10 mS/cm or higher.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the first and second embodiments can suppress aresistance increase rate during high-temperature heating and obtainexcellent low-temperature characteristics.

For this reason, the non-aqueous secondary battery according to thisembodiment is applicable to a wide temperature range from approximately60° C. to −30° C. such as outdoor applications in summer and cold regionuse.

Third Embodiment: Non-Aqueous Electrolyte Solution

According to the third embodiment, in the non-aqueous electrolytesolution according to the first or second embodiment, the PO₂F₂ anionsare preferably obtained by dissociating LiPO₂F₂.

In this manner, the electrolyte solution contains PO₂F₂ anions andlithium ions. By analyzing both ions, it is possible to check whether ornot LiPO₂F₂ as the lithium salt is contained.

Fourth Embodiment: Non-Aqueous Electrolyte Solution

According to a fourth embodiment, in any one of the first to thirdembodiments, the cyclic acid anhydride preferably contains at least oneselected from a group consisting of succinic anhydride, maleicanhydride, and phthalic anhydride. Only one of these cyclic acidanhydrides or a plurality of cyclic acid anhydrides may be contained.Alternatively, any cyclic acid anhydride other than the aforementionedcyclic acid anhydrides may also be contained. As a result, it ispossible to form a robust SEI on the negative electrode and suppress anincrease of the resistance during high-temperature heating.

Fifth Embodiment: Non-Aqueous Electrolyte Solution

According to the fifth embodiment, the cyclic acid anhydride of thenon-aqueous electrolyte solution of the fourth embodiment preferablyincludes at least succinic anhydride. As a result, it is possible tomore effectively form a robust SEI on the negative electrode.

Sixth Embodiment: Non-Aqueous Electrolyte Solution

According to the sixth embodiment, in the non-aqueous electrolytesolution of any one of the first to fifth embodiments, the content ofcyclic acid anhydride is preferably 0.01 mass % or more and 1 mass % orless with respect to the non-aqueous electrolyte solution.

The content of the cyclic acid anhydride is calculated on a masspercentage basis relative to a total mass of all components contained inthe non-aqueous electrolyte solution. More preferably, the content ofthe cyclic acid anhydride is 0.1 mass % or more and 0.7 mass % or less,and furthermore preferably, 0.5 mass % or less with respect to thenon-aqueous electrolyte solution.

As a result, it is possible to more effectively delay generation of gasin the event of overcharge.

Seventh Embodiment: Non-Aqueous Electrolyte Solution

According to the seventh embodiment, in the non-aqueous electrolytesolution of any one of the first to sixth embodiments, the non-aqueoussolvent preferably contains at least acetonitrile.

The non-aqueous solvent may contain acetonitrile alone or any other typeof non-aqueous solvents other than the acetonitrile. Specific examplesof the non-aqueous solvents applicable to this embodiment will bedescribed below. Since the electrolyte solution containing acetonitrilecontains LiPO₂F₂ and cyclic acid anhydride, the SEI is reinforced. Forthis reason, even under a high-temperature environment, dissolution ofthe SEI of the negative electrode is suppressed. Therefore, reductivedecomposition of acetonitrile is suppressed.

Eighth Embodiment: Non-Aqueous Electrolyte Solution

According to an eighth embodiment, the non-aqueous electrolyte solutionof any one of the first to seventh embodiments preferably contains PF₆anions.

In this manner, since PF₆ anions are contained, hydrogen is removed froman α-position of acetonitrile, and generation of HF is promoted, so thatLiF as an element of the negative electrode SEI is effectively formed.In addition, a suitable amount of water more effectively promotes areaction of forming the negative electrode SEI of the cyclic acidanhydride. Therefore, since PF₆ anions are contained, organic/inorganiccomplexation of the negative electrode SEI efficiently proceeds, so thatit is possible to more effectively delay generation of gas duringovercharge.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the eighth embodiment includes, for example, acetonitrile,LiPF₆, SAH, and LiPO₂F₂. In this case, in the non-aqueous secondarybattery, there is no particular limitation in the negative electrode,the positive electrode, the separator, and the battery casing.

Ninth Embodiment: Non-Aqueous Electrolyte Solution

According to a ninth embodiment, in the non-aqueous electrolyte solutionof the eighth embodiment, PF₆ anions are preferably obtained bydissociating LiPF₆.

In this manner, the PF₆ anions and the lithium ions exist in theelectrolyte solution. By analyzing both the ions, it is possible tocheck whether or not the lithium salt and the LiPF₆ are contained.

According to this embodiment, the electrolyte solution is preferablyobtained by mixing LiPO₂F₂ and then adding LiPF₆. In this manner, bydefining the mixing sequence of the electrolyte solution, it is possibleto control the dissolution speed of LiPF₆ and suppress generation of adecomposition product.

The electrolyte solution is preferably obtained by mixing acetonitrileand cyclic acid anhydride and then adding LiPF₆. As a result, it ispossible to suppress an abrupt temperature increase when adding LiPF₆and suppress generation of HF that causes an increase of internalresistance due to sacrificial reaction of the cyclic acid anhydride.

A temperature increase at the time of adding LiPF₆ is preferablysuppressed to 50° C. or lower. As a result, it is possible toappropriately suppress thermal decomposition of LiPF₆ that may begenerated at a temperature of 60° C. or higher.

Tenth Embodiment: Non-Aqueous Electrolyte Solution

According to a tenth embodiment, the non-aqueous electrolyte solution ofany one of the first to ninth embodiments preferably further containslinear carbonate.

The combined use of acetonitrile and linear carbonate advantageouslyacts to suppress association between acetonitrile and LiPF₆.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the tenth embodiment includes, for example, acetonitrile,LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH (1% or less), LiPO₂F₂, and VC (4%or less). In this case, in the non-aqueous secondary battery, there isno particular limitation in the negative electrode, the positiveelectrode, the separator, and the battery casing.

Using the configuration described above, a remarkable effect appears onthe high-temperature durability of the non-aqueous secondary battery, sothat it is possible to obtain a long service life even under ahigh-temperature environment.

Eleventh Embodiment: Non-Aqueous Electrolyte Solution

According to the eleventh embodiment, the linear carbonate of thenon-aqueous electrolyte solution of the tenth embodiment includes, forexample, at least one selected from a group consisting of diethylcarbonate, ethyl methyl carbonate, and dimethyl carbonate.

A specific composition according to the eleventh embodiment is anon-aqueous electrolyte solution containing LiPF₆, acetonitrile (AcN),and diethyl carbonate (DEC). In addition, the lithium salt may includeLiPF₆, LiN(SO₂F)₂, or LiB(C₂O₄)₂(LiBOB). In addition, the non-aqueouselectrolyte solution preferably contains succinic anhydride (SAH).

According to the eleventh embodiment, the non-aqueous electrolytesolution preferably contains LiPF₆ and LiN(SO₂F)₂ as the lithium salt,acetonitrile as the solvent, and cyclic acid anhydride and LiPO₂F₂ asthe additive. As a result, it is possible to suppress cycle degradationat a low temperature by suppressing an interface (film) resistance to below.

In the non-aqueous electrolyte solution described above, a total mass ofthe additive is preferably less than 5%. Note that the additive refersto a general element used as a protection film formation agent such asVC, MAH, SAH, PAH, and ES. As a result, it is possible to suppress aninterface (film) resistance to be low and suppress cycle degradation ata low temperature.

In the non-aqueous electrolyte solution described above, it ispreferable that the amount of LiPO₂F₂ is 0.005 to 1 mass %, and theamount of vinylene carbonate is 4 mass % or less. As a result, bysetting the amount of LiPO₂F₂ and the amount of vinylene carbonate to apredetermined range, it is possible to provide a secondary batteryhaving excellent high-temperature durability and excellentlow-temperature performance.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the eleventh embodiment may be used for a coldregion.

Twelfth Embodiment: Non-Aqueous Electrolyte Solution

According to the twelfth embodiment, in the non-aqueous electrolytesolution of the tenth or eleventh embodiment, the molar mixing ratio ofthe linear carbonate relative to acetonitrile is preferably set to 0.15or higher and 2 or lower.

The combined use of the acetonitrile and the linear carbonateadvantageously acts to suppress association between acetonitrile andLiPF₆. However, the linear carbonate has low polarity. In this regard,the molar mixing ratio of the linear carbonate relative to acetonitrileis adjusted in order to appropriately suppress a decrease of ionicconductivity in a low temperature range even when the linear carbonateis contained.

That is, according to the twelfth embodiment, the molar mixing ratio ofthe linear carbonate relative to the acetonitrile that affectssolubility is adjusted to a particular range. The molar mixing ratio ofthe linear carbonate relative to acetonitrile is expressed as “C/A”,where “A” denotes the number of moles of the acetonitrile and “C” denotethe number of moles of the linear carbonate.

That is, according to the twelfth embodiment, the molar mixing ratio(C/A) of the linear carbonate relative to acetonitrile is adjusted to0.15 or higher and 2 or lower.

According to this embodiment, it is preferable that the followingconditions are satisfied: (1) the non-aqueous electrolyte solutioncontains LiPF₆ and a non-aqueous solvent, and the non-aqueous solventcontains acetonitrile and linear carbonate; (2) the content of LiPF₆ is1.5 mol or less with respect to a non-aqueous solvent of 1 L; (3) themolar mixing ratio of LiPF₆ relative to acetonitrile is 0.08 or higherand 0.16 or lower; and (4) the molar mixing ratio of the linearcarbonate relative to acetonitrile is set to 0.15 or higher and 2 orlower.

As a result, it is possible to more effectively address a tradeoffproblem between prevention of association of LiPF₆ and suppression of adecrease of the ionic conductivity. Specifically, it is possible toobtain an ionic conductivity of 3 mS/cm or higher at a temperature of−30° C. without observing precipitation of white sediments as aggregate.According to this embodiment, preferably, it is possible to obtain anionic conductivity of 3.5 mS/cm or higher at a temperature of −30° C.without inhibiting ion conduction caused by the aggregate. Morepreferably, it is possible to obtain an ionic conductivity of 4 mS/cm orhigher without inhibiting ion conduction caused by the aggregate.Furthermore preferably, it is possible to obtain an ionic conductivityof 4.5 mS/cm or higher without forming the aggregate.

The specific composition and application of the twelfth embodiment aresimilar to those of the eleventh embodiment.

Thirteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the thirteenth embodiment, in the non-aqueous electrolytesolution of the tenth or eleventh embodiment, the molar mixing ratio ofthe linear carbonate relative to acetonitrile is preferably set to 0.25or higher and 2 or lower.

According to the thirteenth embodiment, a limitation is further added tothe twelfth embodiment. As a result, even when the linear carbonate iscontained, it is possible to more effectively and appropriately suppressa decrease of the ionic conductivity in a low temperature range.

Fourteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the fourteenth embodiment, in the non-aqueous electrolytesolution of the tenth or eleventh embodiment, the molar mixing ratio oflinear carbonate relative to acetonitrile is preferably 0.4 or higherand 2 or lower.

According to the fourteenth embodiment, a limitation is further added tothe thirteenth embodiment. As a result, even when the linear carbonateis contained, it is possible to more effectively and appropriatelysuppress a decrease of the ionic conductivity in a low-temperaturerange.

Fifteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the fifteenth embodiment, the non-aqueous electrolytesolution of any one of the first to fourteenth embodiments preferablycontains imide salt.

A technical change at the time of development of the fifteenthembodiment will be described. In the existing electrolyte solution,imide salt such as lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) isemployed in order to improve the ionic conductivity and the cyclecharacteristics of the battery, or the like. Here, the imide salt islithium salt expressed as “LiN(SO₂C_(m)F_(2m+1))₂”, where “m” denotes aninteger of 0 to 8. However, in the non-aqueous electrolyte solutioncontaining imide salt, corrosion proceeds so as to form a solublecomplex with aluminum used as a positive electrode current collector ofthe lithium secondary battery through charging/discharging, so thatelution is generated in the electrolyte solution disadvantageously. Inthis regard, the inventors achieved the present invention to provide anelectrolyte solution capable of suppressing aluminum elution throughcharging/discharging even when the imide salt is contained.

According to the fifteenth embodiment, the non-aqueous electrolytesolution contains a non-aqueous solvent, PO₂F₂ anions, lithium salt, andcyclic acid anhydride, and the lithium salt includes imide salt.

Here, according to the fifteenth embodiment, the non-aqueous electrolytesolution preferably contains the PF₆ anions of the eighth embodiment.The PF₆ anions react with water to produce hydrogen fluoride(hereinafter, referred to as “HF”) and PFs. The fluorine ion derivedfrom HF reacts with aluminum as the positive electrode current collectorto generate a passive film on a surface. As a result, it is possible tosuppress corrosion of the positive electrode containing aluminum andelution of aluminum in the electrolyte solution.

If the acetonitrile is heated in presence of PFs, hydrogen is releasedfrom the α-position so as to promote generation of HF from the PF₆anion. As a result, even under a high-temperature environment wherecorrosion of aluminum proceeds, restoration of the passive film ispromoted, so that it is possible to further suppress elution ofaluminum. That is, it is possible to suppress elution of aluminum evenin charging/discharging.

According to the fifteenth embodiment, the non-aqueous electrolytesolution preferably contains water of 1 ppm or more and 200 ppm or less,and more preferably, 1 ppm or more and 30 ppm or less. This is becausean appropriate amount of water contributes to passivation of aluminum inthe non-aqueous electrolyte solution.

A specific composition of the non-aqueous electrolyte solution accordingto the fifteenth embodiment includes, for example, acetonitrile, imidesalt such as LiN(SO₂F)₂ or LiN(SO₂CF₃)₂, SAH, and LiPO₂F₂. In this case,in the non-aqueous secondary battery, there is no particular limitationin the negative electrode, the positive electrode, the separator, andthe battery casing.

Sixteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the sixteenth embodiment, the imide salt of the non-aqueouselectrolyte solution of the fifteenth embodiment preferably includes atleast one selected from a group consisting of LiN(SO₂F)₂ andLiN(SO₂CF₃)₂. Only one or both of these imide salts may be included.Alternatively, any other imide salt may also be contained.

According to the sixteenth embodiment, since hydrogen is released fromthe α-position of acetonitrile, generation HF from the PF₆ anions ispromoted. Therefore, it is possible to promote passivation of aluminumeven when the imide salt is used.

Note that, according to the sixteenth embodiment, LiPO₂F₂, cyclic acidanhydride, and imide salt are preferably added to the LiPF₆-basedacetonitrile electrolyte solution. As a result, it is possible tosuppress an increase of resistance during high-temperature heating andobtain low-temperature characteristics.

According to the sixteenth embodiment, it is preferable that the imidesalt is added to the LiPF₆-based acetonitrile electrolyte solution suchthat the molarity is set to “LiPO₂F₂ of 0.005 to 1 mass %, cyclic acidanhydride of 0.01 to 1 mass %, and LiPF₆≤imide salt”. As a result, theLiPO₂F₂ and the cyclic acid anhydride reinforce the negative electrodeSEI and suppress an increase of resistance during high-temperatureheating. In addition, excellent low-temperature characteristics areexhibited due to the imide salt.

According to the sixteenth embodiment, it is preferable that LiPO₂F₂ of0.1 to 0.5 mass % with respect to the acetonitrile electrolyte solutionis added, and cyclic acid anhydride of 0.01 to 0.5 mass % with respectto the electrolyte solution is added. In addition, the content of theimide salt (particularly, LiN(SO₂F)₂) is set to 0.5 to 3 mol withrespect to the non-aqueous solvent of 1 L. As a result, LiPO₂F₂ and thecyclic acid anhydride reinforce the negative electrode SEI, so that itis possible to suppress an increase of resistance duringhigh-temperature heating.

Seventeenth Embodiment: Non-Aqueous Electrolyte Solution

According to the seventeenth embodiment, the non-aqueous electrolytesolution of the fifteenth or sixteenth embodiment contains imide salt asa main component of the lithium salt. Preferably, the non-aqueouselectrolyte solution contains the imide salt and lithium salt other thanthe imide salt, as main components, by the same amount.

Here, the “main component” refers to lithium salt contained most in theelectrolyte solution, and a percentage of the molar quantity of theimide salt relative to a total molar quantity of the lithium saltcontained in the electrolyte solution is preferably 50% or higher, andmore preferably 60% or higher.

Among the lithium salts, the imide salt may be contained most alone orlithium salt other than the imide salt may be contained most incombination.

The lithium salt of the non-aqueous electrolyte solution according tothis embodiment may include LiPF₆, LiN(SO₂F)₂, or LiN(SO₂CF₃)₂.

In the non-aqueous electrolyte solution according to this embodiment,elution of aluminum caused charging/discharging is negligible. Inaddition, since the imide salt is contained, it is possible to improvethe ionic conductivity and the battery cycle characteristic.

Therefore, the non-aqueous secondary battery using the non-aqueouselectrolyte solution according to this embodiment is applicable togeneral-purpose products, automobiles, and the like, and is advantageousin that a voltage drop caused by charging/discharging is negligible.

Eighteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the eighteenth embodiment, any one of the non-aqueouselectrolyte solutions of the fifteenth to seventeenth embodimentspreferably contains imide salt with a molarity relationship of“LiPF₆≤imide salt”.

According to the eighteenth embodiment, the content of LiPO₂F₂preferably has a range of 0.001 mass % or more and 1 mass % or less withrespect to the non-aqueous electrolyte solution. In addition, thecontent of the cyclic acid anhydride is preferably 0.01 mass % or moreand 1 mass % or less with respect to the non-aqueous electrolytesolution. Furthermore, imide salt is preferably contained with amolarity relationship of “LiPF₆≤imide salt”. Here, the content ofLiPO₂F₂ and the content of cyclic acid anhydride are expressed as a massratio by assuming that a sum of all components of the non-aqueouselectrolyte solution is set to 100 mass %. In addition, the molaritiesof LiPF₆ and imide salt are measured with respect to the non-aqueoussolvent of “1 L”.

According to the eighteenth embodiment, by defining the content and themolarity as described above, LiPO₂F₂ and cyclic acid anhydride form arobust SEI on the negative electrode. In this manner, since a passivefilm called SEI is formed on the negative electrode, it is possible toeffectively suppress an increase of resistance during high-temperatureheating.

Since imide salt is contained with a molarity relationship of“LiPF₆≤imide salt”, it is possible to suppress a decrease of the ionicconductivity at a low temperature and obtain excellent low-temperaturecharacteristics.

According to this embodiment, the content of LiPO₂F₂ is more preferably0.05 mass % or more and 1 mass % or less with respect to the non-aqueouselectrolyte solution. In addition, the content of cyclic acid anhydrideis more preferably 0.1 mass % or more and 0.5 mass % or less withrespect to the non-aqueous electrolyte solution. Furthermore, thecontent of imide salt is preferably 0.5 mol or more and 3 mol or lesswith respect to the non-aqueous solvent of “1 L”. In this manner, bylimiting the content, it is possible to more effectively suppress anincrease of resistance during high-temperature heating and obtain moreexcellent low-temperature characteristics.

According to the eighteenth embodiment, similar to the sixteenthembodiment, the imide salt preferably includes at least one selectedfrom a group consisting of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂, but not limitedthereto. Only one or both of these imide salts may be included.Alternatively, any other imide salt may also be contained. In this case,the imide salt is preferably contained with a molarity relationship of“LiPF₆≤imide salt”. In addition, the content of the imide salt ispreferably 0.5 mol or more and 3 mol or less with respect to thenon-aqueous solvent of “1 L”.

Using the non-aqueous electrolyte solution containing at least oneselected from a group consisting of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂, it ispossible to effectively suppress reduction of the ionic conductivity ata low temperature range of −10° C. or −30° C. and obtain excellentlow-temperature characteristics.

The non-aqueous electrolyte solution according to the eighteenthembodiment contains acetonitrile, LiPF₆, LiPO₂F₂, imide salt includingat least one selected from a group consisting of LiN(SO₂F)₂ andLiN(SO₂CF₃)₂, and cyclic acid anhydride including at least one selectedfrom a group consisting of succinic anhydride, maleic anhydride, andphthalic anhydride. The cyclic acid anhydride preferably includessuccinic anhydride (SAH).

In this case, there is no particular limitation in the negativeelectrode. Meanwhile, the positive-electrode active material preferablyincludes a lithium-containing compound having layered rock salt typecrystals, but not limited thereto.

There is no particular limitation in the separator and the batterycasing.

The configuration described above has a remarkable effect of suppressingan increase of resistance during high-temperature heating and obtaininglow-temperature characteristics.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the eighteenth embodiment may be used in theoutdoor applications in summer.

Nineteenth Embodiment: Non-Aqueous Electrolyte Solution

According to the nineteenth embodiment, in the non-aqueous electrolytesolution according to any one of the fifteenth to eighteenthembodiments, the content of imide salt is preferably 0.5 mol or more and3 mol or less with respect to the non-aqueous solvent of “1 L”.

According to the nineteenth embodiment, the content of LiPO₂F₂ ispreferably 0.05 mass % or more and 1 mass % or less with respect to thenon-aqueous electrolyte solution. In addition, the content of cyclicacid anhydride is preferably 0.1 mass % or more and 0.5 mass % or lesswith respect to the non-aqueous electrolyte solution. In addition, thecontent of imide salt is preferably 0.5 mol or more and 3 mol or lesswith respect to the non-aqueous solvent of “1 L”.

According to the nineteenth embodiment, similar to the sixteenthembodiment, the imide salt preferably includes at least one selectedfrom a group consisting of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂, but not limitedthereto. Only one or both of these imide salts may be included.Alternatively, any imide salt other than these imide salts may beincluded. In this case, as described in the eighteenth embodiment, theimide salt is preferably contained with a molarity relationship of“LiPF₆≤imide salt”. In addition, the content of the imide salt ispreferably 0.5 mol or more and 3 mol or less with respect to thenon-aqueous solvent of “1 L”.

Using the non-aqueous electrolyte solution containing at least oneselected from a group consisting of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂, it ispossible to effectively suppress reduction of the ionic conductivity ata low temperature range of −10° C. or −30° C. and obtain excellentlow-temperature characteristics.

According to the nineteenth embodiment, a configuration of using LiPF₆and LiN(SO₂F)₂ as the lithium salt and using succinic anhydride (SAH) asthe cyclic acid anhydride may be proposed.

According to the nineteenth embodiment, it is possible to suppress anincrease of resistance during high-temperature heating and obtainlow-temperature characteristics.

According to the eighteenth and nineteenth embodiments, it is possibleto suppress a resistance increase rate to 400% or lower in a full-chargestorage test for 720 hours at a temperature of 60° C. In addition,preferably, it is possible to suppress the resistance increase rate to300% or lower. More preferably, it is possible to suppress theresistance increase rate to 250% or lower.

In measurement of the resistance increase rate, the resistance increaserate was calculated by obtaining a resistance value before thefull-charged storage at a temperature of 60° C. and a resistance valueafter the full-charge storage test at a temperature of 60° C.

According to this embodiment, the ionic conductivity at a temperature of−10° C. is preferably 10 mS/cm or higher. More preferably, the ionicconductivity at a temperature of −10° C. is 12 mS/cm or higher, andfurthermore preferably, the ionic conductivity at a temperature of −10°C. is 12.5 mS/cm or higher.

The specific composition and application of the nineteenth embodimentare similar to, for example, those of the eighteenth embodiment.

Twentieth Embodiment: Non-Aqueous Electrolyte Solution

According to the twentieth embodiment, in the non-aqueous electrolytesolution of the eighth or ninth embodiment, it is preferable that thenon-aqueous solvent contains acetonitrile, and the molar mixing ratio ofPF₆ anions relative to acetonitrile is 0.01 or higher and lower than0.08.

As a result, it is possible to more effectively promote the formationreaction of the negative electrode SEI without generating an insolublecomponent, and more effectively delay generation of gas in the event ofovercharge. That is, according to the twentieth embodiment, it ispossible to promote the reaction of cyclic acid anhydride by water anddelay generation of blister gas in the event of overcharge.

The specific compositions and applications of the twentieth embodimentare similar to, for example, those of the first embodiment.

Twenty First Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty first embodiment, the non-aqueous electrolytesolution of any one of the first to twentieth embodiments preferablyfurther contains cyclic carbonate without no saturated secondary carbon.

A technical change at the time of development of the twenty firstembodiment will be described. For example, if the battery using theexisting acetonitrile electrolyte solution is used or placed at atemperature of 50 to 60° C. (50° C. or higher and 60° C. or lower), thebattery performance is significantly degraded, so that an operationlimitation may be reached in some cases. This is because, ifacetonitrile is heated in presence of PF₆, hydrogen is released from theα-position, and generation of HF is promoted, so that the batteryperformance is abruptly degraded. In this regard, the inventorsdeveloped the present invention in order to reduce the amount of HFgenerated at a temperature of 50° C. to 60° C. That is, according to thetwenty first embodiment, the non-aqueous electrolyte solution does notcontain a non-aqueous solvent having saturated secondary carbon.

The inventors have found that, if the non-aqueous solvent containssaturated secondary carbon, protons are easily released, and this tendsto promote generation of HF at a temperature of 50 to 60° C. That is,since the non-aqueous electrolyte solution according to this embodimentdoes not contain the non-aqueous solvent having saturated secondarycarbon, it is possible to reduce the amount of HF generated at atemperature of 50° C. to 60° C.

Here, the “saturated secondary carbon” refers to a case where the numberof adjacent carbon atoms bonded to a carbon atom is two. In addition,“saturation” means that there is no double or triple bond.

Specific examples of the non-aqueous solvent having the saturatedsecondary carbon include, for example, propylene carbonate, 1,2-butylenecarbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate,1,2-pentylene carbonate, trans-2,3-pentylene carbonate,cis-2,3-pentylene carbonate, γ-valerolactone, γ-carprolactone,δ-carprolactone, 2-methyl tetrahydrofuran, and methyl isopropylcarbonate, but not limited thereto.

It was found that generation of HF is suppressed at a temperature of 50to 60° C. by using the carbonate solvent without saturated secondarycarbon as a non-aqueous solvent.

It was found that promote of generation of HF at a temperature of 50 to60° C. caused by acetonitrile is further suppressed by adding the cycliccarbonate without saturated secondary carbon at a volume ratio higherthan that of acetonitrile.

According to another mode of the twenty first embodiment, thenon-aqueous electrolyte solution contains a non-aqueous solventcontaining acetonitrile and LiPF₆, and an increase rate of thegeneration amount of the hydraulic fluid at 60° C. relative to thegeneration amount of hydraulic fluid at 25° C. is 165% or lower. In thismanner, since it is possible to reduce an increase rate of thegeneration amount of hydraulic fluid at 60° C. relative to thegeneration amount of hydraulic fluid at 25° C., it is possible to obtaina non-aqueous secondary battery suitable for outdoor applications insummer or a tropical area without significantly degrading batteryperformance even when the battery is used or placed outdoor in summer orin the tropical area.

According to the twenty first embodiment, it is preferable that theLiPF₆-based acetonitrile electrolyte solution is diluted with anon-aqueous solvent without saturated tertiary carbon. Since protons areeasily released from the carbonate having saturated secondary carbon(for example, propylene carbonate), generation of HF tends to bepromoted at a temperature of 50 to 60° C. However, if the acetonitrileelectrolyte solution is diluted with a non-aqueous solvent withoutsaturated tertiary carbon, it is possible to effectively suppressgeneration of HF.

The non-aqueous polar solvent without saturated tertiary carbonpreferably has a volume larger than that of acetonitrile. If thenon-aqueous polar solvent without saturated secondary carbon (forexample, ethylene carbonate or vinylene carbonate) is larger than theacetonitrile, it is possible to suppress generation of HF.

As described above, using the non-aqueous electrolyte solution accordingto the twenty first embodiment, it is possible to suppress generation ofHF at a temperature of 50 to 60° C.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the twenty first embodiment includes, for example,acetonitrile, EC, VC, SAH, and LiPO₂F₂. In this case, the positiveelectrode of the non-aqueous secondary battery preferably includes alayered rock salt type. Meanwhile, there is no particular limitation inthe negative electrode, the positive electrode, the separator, and thebattery casing.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the twenty first embodiment is applicable togeneral-purpose products, automobiles, and the like. However, in anycase, the non-aqueous secondary battery according to the twenty firstembodiment is also suitably used for outdoor applications in summer orso-called tropical areas such as the tropical zone or the dry zone. Forexample, according to this embodiment, the configuration of the priorart may be applicable to the battery casing. That is, even when thebattery casing has a configuration similar to that of the prior art, itis possible to obtain a non-aqueous secondary battery suitable foroutdoor applications in summer or tropical areas. Therefore, it ispossible to appropriately suppress an increase of the manufacturing costwithout complicating a manufacturing process.

Twenty Second Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty second embodiment, the cyclic carbonate withoutsaturated secondary carbon in the non-aqueous electrolyte solution ofthe twenty first embodiment may include, for example, ethylenecarbonate, vinylene carbonate, 4,5-dimethyl vinylene carbonate, andfluoroethylene carbonate.

Among them, the cyclic carbonate without saturated secondary carbon isat least one selected from a group consisting of ethylene carbonate andvinylene carbonate.

The specific composition and application of the twenty second embodimentare similar to those of the twenty first embodiment.

Twenty Third Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty third embodiment, the non-aqueous electrolytesolution of the twenty first embodiment contains vinylene carbonate asthe cyclic carbonate without saturated secondary carbon, and the amountof vinylene carbonate contained in the non-aqueous electrolyte solutionis 4 volume % or less.

The additive is indispensable in order to suppress a reductivedecomposition reaction of acetonitrile on the surface of the negativeelectrode. If the additive is insufficient, battery performance isabruptly degraded. Meanwhile, if the film is excessively formed, thisdegrades low-temperature performance.

In this regard, according to the twenty third embodiment, by adjusting adosage of vinylene carbonate as an additive to the aforementioned range,it is possible to suppress an interface (film) resistance to be low andsuppress cycle degradation at a low temperature.

According to the twenty third embodiment, the amount of vinylenecarbonate is preferably less than 3 volume %. As a result, it ispossible to more effectively improve the low temperature durability andprovide a secondary battery having excellent low-temperatureperformance.

According to the twenty third embodiment, it is preferable that thenon-aqueous electrolyte solution contains succinic anhydride (SAH), andthe amount of the succinic anhydride contained in the non-aqueouselectrolyte solution is less than 1 volume %.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the twenty third embodiment includes, for example,acetonitrile, LiPF₆, LiN(SO₂F)₂, or LiN(SO₂CF₃)₂, SAH (1% or less),LiPO₂F₂, and VC (4% or less). In this case, in the non-aqueous secondarybattery, there is no particular limitation in the negative electrode,the positive electrode, the separator, and the battery casing.

Twenty Fourth Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty fourth embodiment, the non-aqueous electrolytesolution according to any one of the first to twenty third embodimentshas an ionic conductivity of 3 mS/cm or higher at a temperature of −30°C.

A technical change at the time of development of the twenty fourthembodiment will be described. For example, in the battery using theexisting electrolyte solution, an operation limitation is reached at atemperature of approximately −20° C. This is because, using the existingelectrolyte solution, the ionic conductivity at a temperature of −20° C.is excessively lowered, and it is difficult to obtain an output powernecessary for the operation. In this regard, the inventors developed thepresent invention in order to obtain, at least an ionic conductivitycorresponding to that of the existing electrolyte solution at atemperature of −20° C. even at a temperature lower than −20° C.(specifically, −30° C.).

The non-aqueous electrolyte solution according to the twenty fourthembodiment preferably contains a non-aqueous solvent and LiPF₆ (lithiumsalt). In addition, the non-aqueous electrolyte solution according tothe twenty fourth embodiment is characterized in that the ionicconductivity at a temperature of −30° C. is equal to or higher than 3mS/cm.

The existing electrolyte solution containing cyclic carbonate, linearcarbonate, and LiPF₆ has an ionic conductivity of approximately 2.7mS/cm at a temperature of −20° C. Therefore, the non-aqueous electrolytesolution according to the twenty fourth embodiment has a −30° C. ionicconductivity equal to or higher than the −20° C. ionic conductivity ofthe existing electrolyte solution. As a result, even when thenon-aqueous secondary battery using the non-aqueous electrolyte solutionaccording to the twenty fourth embodiment is used at a low temperatureof −30° C., it is possible to obtain output power equal to or higherthan that of the battery using the existing electrolyte solution at atemperature of −20° C. Note that the temperature of −20° C. is a lowerlimitation of the operation range of the existing LIB. Therefore, it ispossible to shift the operation limitation to the lower temperaturerange, compared to the prior art.

According to this embodiment, the ionic conductivity at a temperature of−30° C. is preferably 3.5 or higher. More preferably, the ionicconductivity at a temperature of −30° C. is 4.0 or higher. In addition,further preferably, the ionic conductivity at a temperature of −30° C.is 4.5 or higher. As a result, it is possible to shift the operationlimitation to the lower temperature range, compared to the prior art.Therefore, it is possible to obtain more stable low-temperaturecharacteristics.

According to the twenty fourth embodiment, the non-aqueous electrolytesolution preferably contains acetonitrile as a non-aqueous solvent. Thatis, the non-aqueous solvent contains acetonitrile as an indispensablecomponent, and may contain acetonitrile alone or any other type ofnon-aqueous solvents in addition to acetonitrile.

However, in the non-aqueous solvent containing acetonitrile and LiPF₆,there is a tradeoff relationship between prevention of associationbetween acetonitrile and LiPF₆ and suppression of reduction of the ionicconductivity. That is, if prevention of association between acetonitrileand LiPF₆ is promoted, the ionic conductivity decreases. Meanwhile, ifsuppression of reduction of the ionic conductivity is promoted, anaggregate is easily formed.

In this regard, according to the twenty fourth embodiment, a molarmixing ratio of LiPF₆ relative to acetonitrile is adjusted. The molarmixing ratio of LiPF₆ relative to acetonitrile is expressed as “B/A”where “A” denotes the number of moles of acetonitrile, and “B” denotesthe number of moles of LiPF₆.

The molar mixing ratio of LiPF₆ relative to acetonitrile predominantlyaffects the amount of the aggregate. In the twenty fourth embodiment, itis preferable that the content of LiPF₆ is 1.5 mol or less relative tothe non-aqueous solvent of 1 L, and the molar mixing ratio of LiPF₆relative to acetonitrile is 0.08 or higher and 0.16 or lower. As aresult, it is possible to implement a high ionic conductivity.

The non-aqueous solvent preferably contains linear carbonate in additionto acetonitrile. That is, the non-aqueous electrolyte solution containsLiPF₆, acetonitrile as a non-aqueous solvent, and linear carbonate.Although there is no limitation in the type of the linear carbonate, forexample, the linear carbonate may include diethyl carbonate, ethylmethyl carbonate, dimethyl carbonate, or the like.

According to the twenty fourth embodiment, it is preferable that thenon-aqueous electrolyte solution contains LiPF₆ and a non-aqueoussolvent, the content of LiPF₆ is equal to or smaller than 1.5 molrelative to a non-aqueous solvent of 1 L, the non-aqueous solventcontains acetonitrile and linear carbonate, the molar mixing ratio ofLiPF₆ relative to acetonitrile is 0.08 or higher and 0.4 or lower, andthe molar mixing ratio of linear carbonate relative to acetonitrile is0.3 or higher and 2 or lower. In such a composition range, it ispossible to address a tradeoff problem between prevention of associationbetween acetonitrile and LiPF₆ (by increasing linear carbonate) andsuppression of reduction of the ionic conductivity (by increasingacetonitrile).

Using the non-aqueous electrolyte solution according to the twentyfourth embodiment, it is possible to improve the ionic conductivity in alow temperature range, compared to the prior art. Specifically, thenon-aqueous electrolyte solution according to the twenty fourthembodiment has a −30° C. ionic conductivity equal to or higher than the−20° C. ionic conductivity of the existing electrolyte solution.According to the twenty fourth embodiment, it is possible to reduce theamount of the aggregate of PF₆ anions coordinated with two or more Li⁺atoms appearing at a temperature of −10° C. or lower to be smaller thana particular amount.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the twenty fourth embodiment includes, for example,acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, and LiPO₂F₂. In thiscase, in the non-aqueous secondary battery, there is no particularlimitation in the negative electrode, the positive electrode, theseparator, and the battery casing.

The non-aqueous secondary battery using the non-aqueous electrolytesolution according to the twenty fourth embodiment is applicable togeneral-purpose products, automobiles, or the like, suitable for a coldregion. For example, according to this embodiment, a configuration ofthe prior art is applicable to the battery casing. That is, it ispossible to obtain a non-aqueous secondary battery suitable for a coldregion even when the battery casing has a configuration of the priorart. Therefore, it is possible to appropriately suppress an increase ofthe manufacturing cost without complicating a manufacturing process.

Twenty Fifth Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty fifth embodiment, the non-aqueous electrolytesolution according to any one of the first to twenty fourth embodimentspreferably has an ionic conductivity of 10 mS/cm or higher at atemperature of 0° C.

The 0° C. ionic conductivity is higher than the 20° C. ionicconductivity (8.7 to 9.1 mS/cm) of the existing electrolyte solution.The LiPO₂F₂ and the cyclic acid anhydride contribute to formation of theSEI capable of responding to a fast reaction of insertion ordissociation of lithium in the solvent under a low temperature.

It is preferable to satisfy a specific ratio of LiPF₆/AcN (effect to theaggregate amount) and a specific ratio of linear carbonate/AcN (effectto solubility) at the same time. In the AcN electrolyte solution, it ispossible to reduce the amount of the aggregate of PF₆ anions coordinatedwith two or more Li⁺ atoms appearing at a temperature of −10° C. orlower to be smaller than a particular amount.

It is preferable that the non-aqueous electrolyte solution containsLiPF₆ and a non-aqueous solvent, the content of LiPF₆ is equal to orsmaller than 1.5 mol relative to a non-aqueous solvent of 1 L, thenon-aqueous solvent contains acetonitrile and linear carbonate, themolar mixing ratio of LiPF₆ relative to acetonitrile is 0.08 or higherand 0.4 or lower, and the molar mixing ratio of linear carbonaterelative to acetonitrile is 0.3 or higher and 2 or lower. In such acomposition range, it is possible to address a tradeoff problem betweenprevention of association between acetonitrile and LiPF₆ (by increasinglinear carbonate) and suppression of reduction of the ionic conductivityat a low-temperature range (by increasing acetonitrile).

Twenty Sixth Embodiment: Non-Aqueous Electrolyte Solution

According to the twenty sixth embodiment, any one of the non-aqueouselectrolyte solutions of the first to twenty fifth embodimentspreferably has an ionic conductivity of 15 mS/cm or higher at atemperature of 20° C.

It is possible to exhibit high output power performance even when anelectrode active material layer having a high volumetric energy densityis designed. In addition, the ionic conductivity at a temperature of 20°C. is preferably 20 mS/cm or higher, and more preferably, 25 mS/cm orhigher. If the ionic conductivity of the electrolyte solution at atemperature of 20° C. is equal to or higher than 15 mS/cm, lithium ionconduction in the electrode active material layer is sufficientlyperformed. Therefore, it is possible to perform charging/discharging ata large electric current. In addition, although there is no particularlimitation in the upper limit of the ionic conductivity at a temperatureof 20° C., the ionic conductivity is preferably 50 mS/cm or lower, morepreferably 49 mS/cm or lower, and furthermore preferably 48 mS/cm orlower from the viewpoint of suppressing unexpected battery degradationsuch as elution or exfoliation of various battery members. Here, theionic conductivity of the electrolyte solution can be controlled byadjusting, for example, viscosity and/or polarity of the non-aqueoussolvent. Specifically, it is possible to control the ionic conductivityof the electrolyte solution to a high value by mixing a low viscositynon-aqueous solvent and a high polarity non-aqueous solvent.Furthermore, it may be possible to control the ionic conductivity of theelectrolyte solution to a high value by using a non-aqueous solventhaving low viscosity and high polarity. In this manner, according tothis embodiment, it is possible to provide a high ionic conductivity ata temperature of 20° C.

Twenty Seventh Embodiment: Non-Aqueous Electrolyte Solution

First, a technical change at the time of development of the twentyseventh embodiment made by the inventors will be described. Anelectrolyte solution containing acetonitrile as a solvent and LiPF₆ aslithium salt exhibits a high ionic conductivity at the room temperature.However, in a low-temperature range equal to or lower than 0° C., adiscontinuous change occurs in the ionic conductivity of the electrolytesolution, and the output power of the battery using this electrolytesolution is reduced disadvantageously. Such a phenomenon is a problemunique to the non-aqueous electrolyte solution having a high ionicconductivity, and such a problem has not been known until now. In thisregard, the inventors developed the invention in order to stabilize theionic conductivity even at a low temperature by preparing the type ofthe lithium salt and the content of the lithium salt in the electrolytesolution. That is, this embodiment has the following characteristicparts.

The non-aqueous electrolyte solution according to the twenty seventhembodiment contains a non-aqueous solvent and lithium salt. In addition,the activation energy for ionic conduction is preferably 15 kJ/mol orlower at a temperature of −20 to 0° C.

The non-aqueous electrolyte solution according to this embodiment hasactivation energy equal to or smaller than that of the existingelectrolyte solution containing LiPF₆ and a carbonate solvent preferablyat a low-temperature range of 0° C. or lower, and more preferably −10°C. or lower. As a result, it is possible to stabilize the ionicconductivity by suppressing a discontinuous change of the ionicconductivity of the electrolyte solution in a low-temperature range of0° C. or lower. For this reason, even in a case where the non-aqueoussecondary battery using the non-aqueous electrolyte solution accordingto this embodiment is used at a low temperature equal to or lower than0° C., and more preferably, −10° C., it is possible to obtain the outputpower equal to or higher than that of the battery of the existingelectrolyte solution at the room temperature. Therefore, it is possibleto shift the operation limitation to the lower temperature range,compared to the prior art.

According to this embodiment, the activation energy for ionic conductionis preferably 14.5 kJ/mol or lower at a temperature of −20 to 0° C., andmore preferably, 14.0 kJ/mol or lower at a temperature of −20 to 0° C.As a result, it is possible to shift the operation limitation to thelower temperature range and obtain stable low-temperaturecharacteristic, compared to the prior art. Specifically, the compositionof the non-aqueous electrolyte solution according to the twenty seventhembodiment includes, for example, acetonitrile, LiPF₆, LiN(SO₂F)₂, SAH,and LiPO₂F₂. In this case, in the non-aqueous secondary battery, thereis no particular limitation in the negative electrode, the positiveelectrode, the separator, and the battery casing.

Twenty Eighth Embodiment: Non-Aqueous Electrolyte Solution

According to a twenty eighth embodiment, in the non-aqueous electrolytesolution of the twenty seventh embodiment, the activation energy forionic conduction is 15 kJ/mol or lower at a temperature of 0 to 20° C.As a result, it is possible to reduce the activation energy of theelectrolyte solution at a low temperature range of 0° C. or lower andmaintain the activation energy equal to or lower than that of theexisting electrolyte solution even in a temperature range higher than 0°C. Therefore, it is possible to suppress a discontinuous change of theionic conductivity of the electrolyte solution and stabilize the ionicconductivity across a wide temperature range from the low temperature tothe room temperature. For this reason, using the non-aqueous secondarybattery using the non-aqueous electrolyte solution according to thisembodiment, it is possible to obtain the same output power level even inuse at a low temperature or in use at the room temperature range. Inaddition, the non-aqueous secondary battery can be used without beinginfluenced by the temperature condition.

According to the twenty eighth embodiment, the activation energy forionic conduction is preferably 14.5 kJ/mol or lower at a temperature of0 to 20° C., and more preferably, 14.0 kJ/mol or lower at a temperatureof 0 to 20° C. As a result, it is possible to shift the operationlimitation to the wider temperature range, compared to the prior art.

It is possible to lower the activation energy in a low-temperature rangeof −10° C. or lower and in a high-temperature range.

The non-aqueous electrolyte solution preferably contains acetonitrile,LiPO₂F₂, and imide salt. The LiPO₂F₂ suppresses staining of an electrodeas the imide salt functions in a low-temperature range.

Twenty Ninth Embodiment

According to the twenty ninth embodiment, the non-aqueous electrolytesolution according to any one of the first to twenty eighth embodimentspreferably contains a compound expressed as the following formula (1).[Chemical Formula 2]—N═  Formula (1)

The Formula (1) of the twenty ninth embodiment corresponds to a minimumunit of a nitrogen-containing cyclic compound expressed in the followingthirtieth embodiment.

Specifically, the composition of the non-aqueous electrolyte solutionaccording to the twenty ninth embodiment includes, for example,acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, and MBTA.In this case, the positive electrode of the non-aqueous secondarybattery preferably includes a layered rock salt type. Meanwhile, thereis no particular limitation in the negative electrode, the positiveelectrode, the separator, and the battery casing.

Thirtieth Embodiment: Non-Aqueous Electrolyte Solution

According to the thirtieth embodiment, the compound of Formula (1) ofthe non-aqueous electrolyte solution of the twenty ninth embodiment ispreferably a nitrogen-containing cyclic compound. Preferably, thenitrogen-containing cyclic compound is a bicyclic nitrogen-containingcyclic compound.

Specifically, the nitrogen-containing cyclic compound preferablyincludes a nitrogen-containing cyclic compound without steric hindrancearound an unshared electron pair. As a specific example, for example,the nitrogen-containing cyclic compound may be expressed as thefollowing Formula (9):

where “R¹” denotes an alkyl group having 1 to 4 carbon atoms, an arylgroup, a propargyl group, a phenyl group, a benzyl group, a pyridylgroup, an amino group, a pyrrolidylmethyl group, a trimethylsilyl group,a nitrile group, an acetyl group, a trifluoroacetyl group, achloromethyl group, a methoxymethyl group, an isocyanomethyl group, amethylsulfonyl group, a phenylsulfonyl group, a sulfonyl azide group, apyridylsulfonyl group, a 2-(trimethylsilyl)etoxycarbonyloxy group, abis(N,N′-alkyl)aminomethyl group, or a bis(N,N′-alkyl)aminoethyl group,“R²” denotes an alkyl group having 1 to 4 carbon atoms, afluorine-substituted alkyl group having 1 to 4 carbon atoms, an alkoxygroup having 1 to 4 carbon atoms, a fluorine-substituted alkoxy grouphaving 1 to 4 carbon atoms, a nitrile group, a nitro group, an aminogroup, or halogen atoms, and “k” denotes an integer of 0 to 4.

In the nitrogen-containing organic compound expressed in theaforementioned Formula (9), it is particularly preferable that “R¹═CH₃,and k=0”

The content of the nitrogen-containing cyclic compound of theelectrolyte solution according to the thirtieth embodiment is preferably0.01 to 10 mass %, more preferably 0.02 to 5 mass %, and furthermorepreferably 0.03 to 3 mass %, but not limited thereto, with respect to atotal amount of the electrolyte solution. According to this embodiment,the nitrogen-containing cyclic compound forms a robust SEI by when it isused together with an organic lithium salt having an oxalic acid group.

The non-aqueous electrolyte solution preferably contains LiPO₂F₂ of0.005 to 1 mass %, a nitrogen-containing cyclic compound of 0.01 to 1mass %, and cyclic acid anhydride of 0.01 to 1 mass %. Since thenitrogen-containing cyclic compound is contained, elution of metalderived from the positive-electrode active material is suppressed, andan increase of interface resistance of the positive electrode issuppressed. Therefore, since a certain amount of LiPO₂F₂ and cyclic acidanhydride are contained, it is possible to suppress growth of atransition metal precipitated on the negative electrode.

In the twenty ninth and thirtieth embodiments, a specific compositionincludes 1-methyl-1H-benzotriazole (MBTA). Using the nitrogen-containingcyclic compound without N—H bond, it is possible to prevent hydrogenfrom being released in a high-temperature cycle and suppress generationof gas.

<Non-Aqueous Solvent>

Here, the non-aqueous solvent will be described. The “non-aqueoussolvent” as used in this embodiment refers to an element of theelectrolyte solution other than the lithium salt and the additive.

According to this embodiment, while acetonitrile is preferably containedas an essential component, any non-aqueous solvent other than theacetonitrile may also be contained. The non-aqueous solvent other thanthe acetonitrile may include, for example, alcohols such as methanol orethanol, an aprotic solvent, or the like. Among them, the aprotic polarsolvent is preferable.

Specifically, among the non-aqueous solvents, the aprotic solvent mayinclude, for example, cyclic carbonate such as ethylene carbonate,propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylenecarbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate,trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylenecarbonate, 4,5-dimethyl vinylene carbonate, and vinyl ethylenecarbonate; fluoroethylene carbonate such as 4-fluoro-1,3-dioxolan-2-one,4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one,trans-4,5-difluoro-1,3-dioxolan-2-one,4,4,5-trifluoro-1,3-dioxolan-2-one,4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one; lactone such asγ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone,δ-caprolactone, and ε-caprolactone; a sulfur compound such as ethylenesulfite, propylene sulfite, butylene sulfite, pentene sulfite,sulfolane, 3-sulfolane, 3-methyl sulfolane, 1,3-propane sultone,1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide,tetramethylene sulfoxide, and ethyleneglycol sulfite; cyclic ethers suchas tetrahydrofuran, 2-methyl tetrahydrofuran, 1,4-dioxane, and1,3-dioxane; linear carbonates such as ethyl methyl carbonate, dimethylcarbonate, diethyl carbonate, methylpropyl carbonate, methyl isopropylcarbonate, dipropyl carbonate, methyl butyl carbonate, dibutylcarbonate, ethyl propylene carbonate, and methyl trifluoroethylcarbonate; linear fluorinated carbonate such as trifluorodimethylcarbonate, trifluorodiethyl carbonate, and trifluoroethyl methylcarbonate; mononitriles such as propionitrile, butyronitrile,valeronitrile, benzonitrile, and acrylonitrile; alkoxy-substitutednitrile such as methoxyacetonitrile and 3-methoxypropionitrile;dinitrile such as malononitrile, succinonitrile, glutaronitrile,adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane,1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane,2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane,1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;cyclic nitrile such as benzonitrile; linear ester such as methylpropionate; linear ether such as dimethoxyethane, diethyl ether,1,3-dioxolane, diglyme, triglyme, and tetraglyme; fluorinated ether suchas Rf⁴—OR⁵ (where “Rf⁴” is a fluorine atom-containing alkyl group and“R⁵” is an organic group that may contain a fluorine atom); ketone suchas acetone, methyl ethyl ketone, and methyl isobutyl ketone; halide suchas fluoride thereof, or the like. These materials are used solely or incombination of two or more materials.

Among these and other non-aqueous solvents, at least one selected from agroup consisting of cyclic carbonate and linear carbonate is preferablyemployed. Here, although the cyclic carbonate and the linear carbonatehave been exemplified in the aforementioned description, only one ofthem may be employed, or two or more of them may be employed (forexample, two or more of the cyclic carbonates described above, two ormore of the linear carbonates described above, or a combination of twoor more carbonates selected from one or more cyclic carbonates describedabove and one or more linear carbonates described above). Among them,the cyclic carbonate more preferably includes ethylene carbonate,propylene carbonate, vinylene carbonate, or fluoroethylene carbonate,and the linear carbonate more preferably includes ethyl methylcarbonate, dimethyl carbonate, or diethyl carbonate.

The acetonitrile is electrochemically susceptible to reductivedecomposition. For this reason, it is preferable to perform at least oneof a process of mixing the acetonitrile with another solvent or aprocess of adding an electrode protection additive for forming aprotection film on the electrode.

In order to improve an ionization degree of the lithium saltcontributing to charging/discharging of the non-aqueous secondarybattery, the non-aqueous solvent preferably contains one or more cyclicaprotic polar solvents and more preferably contains one or more cycliccarbonates.

According to this embodiment, it is preferable that the non-aqueouselectrolyte solution contains an organic chlorine compound as a chlorideadduct of the cyclic carbonate.

Here, according to this embodiment, the cyclic carbonate preferablyincludes vinylene carbonate (VC), but not limited thereto.

According to this embodiment, the organic chlorine compound preferablyincludes at least one selected from a group consisting of compoundsexpressed in the following formulas (4) to (7).

The organic chlorine compounds expressed in Formulas (4) to (7) may beused alone, or two or more different types of organic chlorine compoundsmay be used in combination.

Using the chloride adduct derived from vinylene carbonate belonging to agroup that is easily reduced among the non-aqueous solvents, the SEIformation reaction reliably proceeds before reductive decomposition ofacetonitrile. Therefore, it is possible to further promote reinforcementof the negative electrode SEI and more effectively improve thehigh-temperature durability of the non-aqueous secondary battery.

Among these and other non-aqueous solvents, it is preferable to use atleast one selected from a group consisting of cyclic carbonates andlinear carbonates. Here, as the cyclic carbonate and the linearcarbonate, only one of those described above may be selected, or two ormore of them may be employed in combination (for example, two or morecyclic carbonates described above, two or more linear carbonatesdescribed above, or a combination of two or more carbonates selectedfrom one or more cyclic carbonates described above and one or morelinear carbonates described above). Among them, the cyclic carbonatemore preferably includes ethylene carbonate, propylene carbonate,vinylene carbonate, or fluoroethylene carbonate, and the linearcarbonate more preferably includes ethyl methyl carbonate, dimethylcarbonate, or diethyl carbonate.

<Whole Configuration of Non-Aqueous Secondary Battery>

The non-aqueous electrolyte solution according to this embodiment may beused in a non-aqueous secondary battery. In the non-aqueous secondarybattery according to this embodiment, there is no particular limitationin the negative electrode, the positive electrode, the separator, andthe battery casing.

The non-aqueous secondary battery according to this embodiment mayinclude a lithium ion battery, but not limited thereto, having apositive electrode containing a positive electrode material capable ofabsorbing and discharging lithium ions as a positive-electrode activematerial, and a negative electrode containing a negative electrodematerial capable of absorbing and discharging lithium ions and anegative electrode material including at least one selected from a groupconsisting of metal lithium as a negative-electrode active material.

Specifically, the non-aqueous secondary battery according to thisembodiment may be the non-aqueous secondary battery illustrated in FIGS.1 and 2. Here, FIG. 1 is a plan view schematically illustrating thenon-aqueous secondary battery, and FIG. 2 is a cross-sectional viewtaken along the line A-A of FIG. 1.

The non-aqueous secondary battery 100 of FIGS. 1 and 2 includes pouchtype cells. The non-aqueous secondary battery 100 is configured byhousing a laminated electrode structure formed by stacking a positiveelectrode 150 and a negative electrode 160 by interposing a separator170 and a non-aqueous electrolyte solution (not shown) in a space 120 ofa battery casing 110 having a pair of aluminum laminate films. Thebattery casing 110 is sealed by thermally fusing the upper and loweraluminum laminate films around their outer peripheries. The non-aqueouselectrolyte solution is impregnated into the stacking component formedby sequentially stacking the positive electrode 150, the separator 170,and negative electrode 160.

The aluminum laminate film of the battery casing 110 is preferablyformed by coating both sides of an aluminum foil with polyolefin-basedresin.

The positive electrode 150 is connected to a positive electrode leadbody 130 inside the non-aqueous secondary battery 100. Although notshown in the drawings, the negative electrode 160 is also connected to anegative electrode lead body 140 inside the non-aqueous secondarybattery 100. In addition, in each of the positive electrode lead body130 and the negative electrode lead body 140, one end side is exposed tothe outside of the battery casing 110 in order to facilitate connectionof external devices or the like. Such an ionomer portion is thermallyfused together with one side of the battery casing 110.

In the non-aqueous secondary battery 100 illustrated in FIGS. 1 and 2,each of the positive electrode 150 and the negative electrode 160 has asingle laminated electrode structure. However, the number of layers inthe positive electrode 150 and the negative electrode 160 mayappropriately increase depending on capacity design. In a case whereeach of the positive electrode 150 and the negative electrode 160 is alaminated electrode structure having a plurality of layers, taps of thesame polarity are bonded through welding or the like, and they arebonded to one lead body through welding or the like, so that the leadmay be extracted to the outside of the battery. As a tap of the samepolarity, an exposed portion of the current collector or the like may beused. Alternatively, a metal piece may be welded to the exposed portionof the current collector, or any other type may be employed.

The positive electrode 150 includes a positive-electrode active materiallayer formed of a positive electrode mixture and a positive electrodecurrent collector. The negative electrode 160 includes anegative-electrode active material layer formed of a negative electrodemixture and a negative electrode current collector. The positiveelectrode 150 and the negative electrode 160 are arranged such that thepositive-electrode active material layer and the negative-electrodeactive material layer face each other by interposing the separator 170.

Each of these members may be formed by using materials of the lithiumion battery of the prior art, but not limited thereto. Each member ofthe non-aqueous secondary battery will now be described in details.

<Non-Aqueous Electrolyte Solution>

If the non-aqueous electrolyte solution has the characteristic partsdescribed in each of the aforementioned embodiments, materials used inthe non-aqueous electrolyte solution of the lithium ion battery of theprior art may be employed.

The “non-aqueous electrolyte solution” according to this embodimentrefers to an electrolyte solution containing water of 1% or less.Preferably, the ratio of water is 300 ppm or less, and more preferably,200 ppm or less.

The “non-aqueous solvent” has been described above, and will not bedescribed repeatedly.

<Lithium Salt>

The lithium salt used in the non-aqueous electrolyte solution accordingto this embodiment is not particular limited unless specified otherwisein individual embodiments. For example, according to this embodiment,the lithium salt includes LiPF₆ or imide salt.

The imide salt is lithium salt expressed as “LiN(SO₂C_(m)F_(2m+1))₂”(where “m” denotes an integer of 0 to 8). Specifically, as described inthe fourth embodiment, the imide salt preferably includes at least oneselected from a group consisting of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂.

The imide salt may include a fluorine-containing inorganic lithium saltother than LiPF₆. The imide salt may include a fluorine-containinginorganic lithium salt such as LiBF₄, LiAsF₆, Li₂SiF₆, LiSbF₆, andLi₂B₁₂F_(b)H_(12-b) (where “b” denotes an integer of 0 to 3). The“fluorine-containing inorganic lithium salt” refers to lithium salt thatdoes not contain a carbon atom in the anion but contains a fluorine atomin the anion. The fluorine-containing inorganic lithium salt isexcellent in that it forms a passive film on a surface of a metal foilas the positive electrode current collector and suppresses corrosion ofthe positive electrode current collector. Such a fluorine-containinginorganic lithium salt may be used alone or in combination of two ormore. A representative fluorine-containing inorganic lithium salt isLiPF₆ which releases the PF₆ anions when dissolved.

The content of the fluorine-containing inorganic lithium salt in thenon-aqueous electrolyte solution according to this embodiment is notparticularly limited, but is preferably 0.1 mol or more, more preferably0.2 mol or more, and furthermore preferably 0.25 mol or more withrespect to the non-aqueous solvent of 1 L. If the content of thefluorine-containing inorganic lithium salt is within the aforementionedrange, it is possible to increase the ionic conductivity and exhibithigh output power characteristics.

The non-aqueous electrolyte solution according to this embodiment mayfurther contain an organic lithium salt. The “organic lithium salt”refers a lithium salt containing a carbon atom in the anion.

The organic lithium salt may include an organic lithium salt having anoxalic acid group. Specific examples of the organic lithium salt havingthe oxalic acid group may include, for example, LiB(C₂O₄)₂, LiBF₂(C₂O₄),LiPF₄(C₂O₄), or LiPF₂(C₂O₄)₂. Among them, the lithium salt preferablyincludes at least one selected from a group consisting of LiB(C₂O₄)₂ andLiBF₂(C₂O₄). In addition, it is more preferable to use one of theorganic lithium salts or two or more of the organic lithium saltsdescribed above together with the fluorine-containing inorganic lithiumsalt.

The amount of the organic lithium salt having an oxalic acid group to beadded to the non-aqueous electrolyte solution is preferably 0.005 mol ormore, more preferably 0.02 mol or more, and furthermore preferably 0.05mol or more per 1 L of the non-aqueous solvent of the non-aqueouselectrolyte solution in order to more reliably guarantee its use effect.However, if the amount of the organic lithium salt having the oxalicacid group in the non-aqueous electrolyte solution described above isexcessively large, the lithium salt may be precipitated. Therefore, theamount of the organic lithium salt having the oxalic acid group added tothe non-aqueous electrolyte solution described above is preferably lessthan 0.1 mol, more preferably less than 0.5 mol, and furthermorepreferably less than 0.2 mol per 1 L of the non-aqueous solvent of thenon-aqueous electrolyte solution.

It is known that the organic lithium salt having the oxalic acid groupdescribed above is insoluble in an organic solvent having a lowpolarity, and particularly linear carbonate. The organic lithium salthaving the oxalic acid group contains a small amount of lithium oxalatein some cases. In addition, even when it is mixed as a non-aqueouselectrolyte solution, it reacts with a small amount water contained inother source materials, so that white sediments of lithium oxalate aregenerated initially in some cases. Therefore, the content of the lithiumoxalate in the non-aqueous electrolyte solution according to thisembodiment is preferably 0 to 500 ppm, but not particularly limitedthereto.

As the lithium salt according to this embodiment, any lithium salttypically used in the non-aqueous secondary battery other than thosedescribed above may be added as a supplement. A specific example of theother lithium salts may include, for example, an inorganic lithium saltthat does not contain a fluorine atom in the anion, such as LiClO₄,LiAlO₄, LiAlCl₄, LiB₁₀Cl₁₀, or chloroborane Li; an organic lithium saltsuch as LiCF₃SO₃, LiCF₃CO₂, Li₂C₂F₄(SO₃)₂, LiC(CF₃SO₂)₃,LiC_(n)F_(2n+1)SO₃ (n≥2), low fat carboxylic acid lithium, ortetraphenylboric acid lithium; an organic lithium salt expressed as“LiPF_(n)(C_(p)F_(2p+1))_(6-n)” (where “n” denotes an integer of 1 to 5,and “p” denotes an integer of 1 to 8), such as LiPF₅(CF₃); an organiclithium salt expressed as “LiBF_(q)(CsF_(2s+1))_(4-q)” (where “q”denotes an integer of 1 to 3, and “s” denotes an integer of 1 to 8),such as LiBF₃(CF₃); a lithium salt bonded to a polyvalent anion; or anorganic lithium salt expressed as the following formulas (10a), (10b),and (10c):LiC(SO₂R⁶)(SO₂R⁷)(SO₂R⁸)  (10 a)LiN(SO₂OR⁹)(SO₂OR¹⁰)  (10 b)LiN(SO₂R¹¹)(SO₂OR¹²)  (10 c)(where the factors R⁶, R⁷, R⁸, R⁹, R¹⁹, R¹¹, and R¹² may be the same ordifferent, and denote a perfluoroalkyl group having a carbon number of 1to 8) and the like. One or more of these materials may be used togetherwith LiPF₆.

(Other Optional Additives)

According to this embodiment, the non-aqueous electrolyte solution mayappropriately contain an optional additive selected from a groupconsisting of acid anhydride, sulfonic ester, diphenyl disulfide,cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphateester (such as ethyl diethyl phosphono acetate (EDPA):(C₂H₅O)₂(P═O)—CH₂(C═O)OC₂H₅, tris(trifluoroethyl) phosphaste (TFEP):(CF₃CH₂O)₃P═O, triphenyl phosphate (TPP): (C₆H₅O)₃P═O, triarylphosphate: (CH₂═CHCH₂O)₃P═O), and any derivative of these compounds. Inparticular, the aforementioned phosphate ester has an effect ofsuppressing a side reaction during storage, which is effective.

The non-aqueous electrolyte solution according to this embodiment mayinclude a nitrogen-containing cyclic compound without steric hindrancearound an unshared electron pair as described in the twenty fifthembodiment.

<Positive Electrode>

The positive electrode 150 includes a positive-electrode active materiallayer formed of a positive electrode mixture and a positive electrodecurrent collector. Any electrode may be employed as the positiveelectrode 150 without a particular limitation, including those known inthe art, as long as it can serve as a positive electrode of thenon-aqueous secondary battery.

The positive-electrode active material layer contains apositive-electrode active material and optionally further contains aconductive aid and a binder.

The positive-electrode active material layer preferably contains amaterial capable of absorbing and releasing lithium ions as apositive-electrode active material. The positive-electrode activematerial layer preferably contains a conductive aid and a binder asnecessary in addition to the positive-electrode active material. Usingthese materials, it is possible to obtain a high voltage and a highenergy density, advantageously.

The positive-electrode active material may include a lithium-containingcompound expressed as the following formulas (11a) and (11b) and anyother lithium-containing compound,Li_(x)MO₂  (11a)Li_(y)M₂O₄  (11b)

(where “M” denotes one or more metal elements including at least one oftransition metal elements, “x” denotes a number of 0 to 1.1, and “y”denotes a number of 0 to 2).

The lithium-containing compound expressed in the formulas (11a) and(11b) may include, for example, lithium cobalt oxide such as LiCoO₂,lithium manganese oxide such as LiMnO₂, LiMn₂O₄, and Li₂Mn₂O₄, lithiumnickel oxide such as LiNiO₂, lithium-containing composite metal oxidesuch as Li_(z)MO₂ (where “M” contains a transition metal elementcontaining at least one selected from a group consisting of Ni, Mn, andCo, or two or more metal elements selected from a group consisting ofNi, Mn, Co, Al, and Mg, and “z” denotes a number greater than 0.9 andsmaller than 1.2), or the like.

The lithium-containing compound other than those of the formulas (11a)and (11b) are not particularly limited as long as it contains lithium.Such a lithium-containing compound may include, for example, a compositeoxide containing lithium and a transition metal element, metalchalcogenide having lithium, a phosphate metal compound containinglithium and a transition metal element, or a silicate metal compoundcontaining lithium and a transition metal element (for example,Li_(t)M_(u)SiO₄ where “M” is defined in Formula (12a), “t” denotes anumber of 0 to 1, and “u” denotes a number of 0 to 2). In order toobtain a higher voltage, the lithium-containing compound is preferably aphosphate metal compound or a composite oxide particularly containinglithium and a transition metal element including at least one selectedfrom a group consisting of cobalt (Co), nickel (Ni), manganese (Mn),iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), andtitanium (Ti).

More specifically, the lithium-containing compound preferably includes acomposite oxide containing lithium and a transition metal element, metalchalcogenide containing lithium and a transition metal element, or aphosphate metal compound containing lithium. For example, thelithium-containing compound may be expressed by the following Formulas(12a) and (12b):Li_(v)M^(I)D₂  (12 a)Li_(w)M^(II)PO₄  (12 b)

(where “D” denotes an oxygen or charlcogen element, “M^(I)” and “M^(II)”denotes one or more transition metal elements, “v” and “w” values aredefined by a charging/discharging state of the battery, “v” denotes anumber of 0.05 to 1.10, and “w” denotes a number of 0.05 to 1.10).

The lithium-containing compound expressed in the aforementioned Formula(12a) has a layered structure, and the compound expressed in theaforementioned Formula (12b) has an olivine structure. For the purposeof stabilizing a structure or the like, such a lithium-containingcompound may be obtained by substituting a part of the transition metalelement with Al, Mg, or another transition metal element, inserting sucha metal element into a crystalline interface, substituting a part of theoxygen atom with a fluorine atom or the like, coating anotherpositive-electrode active material on at least a part of the surface ofthe positive-electrode active material, or the like.

The positive-electrode active material according to this embodiment mayinclude only the lithium-containing compound described above, or mayadditionally include another positive-electrode active material togetherwith the lithium-containing compound.

Such other positive-electrode active materials may include, for example,a metal oxide or metal chalcogenide having a tunnel structure or alayered structure, sulfur, a conductive polymer, or the like. The metaloxide or metal chalcogenide having a tunnel structure or a layeredstructure may include, for example, oxide, sulfide, selenide, or thelike of metal other than lithium, such as MnO₂, FeO₂, FeS₂, V₂O₅, V₆O₁₃,TiO₂, TiS₂, MoS₂, and NbSe₂. The conductive polymer may include, forexample, polyaniline, polythiophene, polyacetylene, or polypyrrole.

The other positive-electrode active materials described above may beused alone or in combination of two or more materials without aparticular limitation. However, the aforementioned positive-electrodeactive material layer preferably contains at least one transition metalelement selected from a group consisting of Ni, Mn, and Co because it ispossible to reversibly and stably absorb and release lithium ions andachieve a high energy density.

In a case where the lithium-containing compound and anotherpositive-electrode active material are used in combination as thepositive-electrode active material, a ratio therebetween, that is, aratio of the lithium-containing compound relative to the wholepositive-electrode active material is preferably 80 mass % or more, andmore preferably 85 mass % or more.

The conductive aid may include, for example, carbon black such asgraphite, acetylene black, and ketjen black, or a carbon fiber. Thecontent of the conductive aid is preferably 10 parts by mass or less,and more preferably 1 to 5 parts by mass with respect to 100 parts bymass of the positive-electrode active material.

The binder may include, for example, polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), polyacrylic acid, styrene butadienerubber, or fluororubber. The content of the binder is preferably 6 partsby mass or less, and more preferably 0.5 to 4 parts by mass with respectto 100 parts by mass of the positive-electrode active material.

The positive-electrode active material layer is formed by applying, tothe positive electrode current collector, positive electrodemixture-containing slurry obtained by dispersing a positive electrodemixture obtained by mixing the positive-electrode active material, theconductive aid, and the binder as necessary into a solvent, drying it(to remove the solvent), and pressing it as necessary. Such a solventmay include those used in the prior art without a particular limitation.For example, the solvent may include N-methyl-2-pyrrolidone,dimethylformamide, dimethylacetamide, water, or the like.

The positive electrode current collector includes, for example, a metalfoil such as an aluminum foil, a nickel foil, and a stainless foil. Thepositive electrode current collector may have a surface coated withcarbon or may be meshed. The thickness of the positive electrode currentcollector is preferably 5 to 40 μm, more preferably 7 to 35 μm, andfurthermore preferably 9 to 30 μm.

<Negative Electrode>

The negative electrode 160 includes a negative-electrode active materiallayer formed of a negative electrode mixture, and a negative electrodecurrent collector. Any electrode may be employed as the negativeelectrode 160 without a particular limitation, including those known inthe art, as long as it can serve as a negative electrode of anon-aqueous secondary battery.

The negative-electrode active material layer preferably contains amaterial capable of absorbing lithium ions as a negative-electrodeactive material at an electric potential lower than 0.4 V vs. Li/Li⁺from the viewpoint of increasing the battery voltage. Thenegative-electrode active material layer preferably contains aconductive aid and a binder, as necessary, together with thenegative-electrode active material.

The negative-electrode active material may include, for example, acarbon material such as amorphous carbon (hard carbon), artificialgraphite, natural graphite, graphite, pyrolytic carbon, coke, glassycarbon, a sintered product of an organic polymer compound, mesocarbonmicrobeads, a carbon fiber, activated carbon, graphite, carbon colloid,and carbon black, metal lithium, metal oxide, metal nitride, lithiumalloy, tin alloy, silicon alloy, an intermetallic compound, an organiccompound, an inorganic compound, a metal complex, an organic polymercompound, or the like.

The negative-electrode active material may be used alone or incombination of two or more materials.

The conductive aid may include, for example, carbon black such asgraphite, acetylene black, and ketjen black, or a carbon fiber. Thecontent of the conductive aid is preferably 20 parts by mass or less,and more preferably 0.1 to 10 parts by mass with respect to 100 parts bymass of the negative-electrode active material.

The binder may include, for example, PVDF, PTFE, polyacrylic acid,styrene butadiene rubber, or fluororubber. The content of the binder ispreferably 10 parts by mass or less, and more preferably 0.5 to 6 partsby mass with respect to 100 parts by mass of the negative-electrodeactive material.

The negative-electrode active material layer is formed by applying, tothe negative electrode current collector, negative electrodemixture-containing slurry obtained by dispersing a negative electrodemixture obtained by mixing the negative-electrode active material, theconductive aid, and the binder as necessary into a solvent, drying it(to remove the solvent), and pressing it as necessary. Such a solventmay include those used in the prior art without a particular limitation.For example, the solvent may include N-methyl-2-pyrrolidone,dimethylformamide, dimethylacetamide, water, or the like.

The negative electrode current collector includes, for example, a metalfoil such as a copper foil, a nickel foil, and a stainless foil. Thenegative electrode current collector may have a surface coated withcarbon or may be meshed. The thickness of the negative electrode currentcollector is preferably 5 to 40 μm, more preferably 6 to 35 μm, andfurthermore preferably 7 to 30 μm.

<Separator>

The non-aqueous secondary battery 100 according to this embodimentpreferably has a separator 170 between the positive electrode 150 andthe negative electrode 160 in order to prevent short-circuiting betweenthe positive electrode 150 and the negative electrode 160 or givingsafety protection such as shutdown. The separator 170 may be thoseprovided in a non-aqueous secondary battery known in the art without alimitation, and is preferably an insulating thin film having high ionpermeability and a strong mechanical strength. The separator 170 mayinclude, for example, a woven fabric, a non-woven fabric, a microporousmembrane made from a synthetic resin, or the like. Among them, themicroporous membrane made from a synthetic resin is preferable.

The microporous membrane made from a synthetic resin may include, forexample, a microporous membrane containing polyethylene or polypropyleneas a main component, or a polyolefin-based microporous membrane such asa microporous membrane containing both of these polyolefins. Thenonwoven fabric may include, for example, a porous membrane formed ofglass, ceramic, polyolefin, polyester, polyamide, liquid crystalpolyester, and heat-resistant resin such as aramid.

The separator 170 may be formed by stacking a single layer or aplurality of layers of one type of the microporous membrane or may be astack of two or more microporous membranes. The separator 170 may beformed by stacking a mixed resin material obtained by melting andkneading two or more resin materials in a single layer or a plurality oflayers.

<Battery Casing>

A configuration of the battery casing 110 of the non-aqueous secondarybattery 100 according to this embodiment may include some battery casingcomponents, such as a battery can and a laminate film package, but notlimited thereto. The battery can may include a metal can such as a steelcan or an aluminum can. The laminate film package may include, forexample, a laminate film having a three-layered structure of hot-meltingresin/metal film/resin.

The laminate film package may be used as a package by overlapping a pairof films while directing the hot-melting resin side inward or folding apair of films to allow the hot-melting resin side to face inward, andthermally sealing both ends. In a case where the laminate film packageis employed, the positive electrode lead body 130 (or a positiveelectrode terminal and a lead tap connected to the positive electrodeterminal) may be connected to the positive electrode current collector,and the negative electrode lead body 140 (or a negative electrodeterminal and a lead tap connected to the negative electrode terminal)may be connected to the negative electrode current collector. In thiscase, the laminate film package may be sealed while ends of the positiveelectrode lead body 130 and the negative electrode lead body 140 (or thelead tap connected to each positive electrode terminal and negativeelectrode terminal) are exposed to the outside of the package.

<Method of Producing Non-aqueous Electrolyte Solution>

The non-aqueous electrolyte solution according to this embodiment may beproduced by mixing lithium salt, cyclic acid anhydride, and additivesdescribed in each embodiment with acetonitrile as a non-aqueous solventusing an arbitrary method. Note that the content of each additive isdescribed in each embodiment.

<Method of Manufacturing Battery>

The non-aqueous secondary battery 100 according to this embodiment ismanufactured by using the non-aqueous electrolyte solution describedabove, the positive electrode 150 having a positive-electrode activematerial layer formed on one or both sides of the current collector, anegative electrode 160 having a negative-electrode active material layerformed on one or both sides of the current collector, the battery casing110, and the separator 170 as necessary on the basis of a method knownin the art.

First, a stacking component including the positive electrode 150, thenegative electrode 160, and the separator 170 as necessary is formed.For example, a winding structure stacking component may be formed bywinding a stack of the long positive electrode 150 and the long negativeelectrode 160 while interposing a long separator between the positiveelectrode 150 and the negative electrode 160. A layered structurestacking component may be formed by alternately stacking positiveelectrode sheets and a negative electrode sheets obtained by cutting thepositive electrode 150 and the negative electrode 160 to a plurality ofsheets having constant areas and shapes while interposing separatorsheets. A layered structure stacking component may be formed by foldinga long separator in an overlapping manner and alternately inserting thepositive electrode sheets and the negative electrode sheets between theseparators.

Then, the stacking component described above is housed in the batterycasing 110 (battery casing), and the electrolyte solution according tothis embodiment is injected into the battery casing. In addition, thestacking component is impregnated into an electrolyte solution, andsealing is performed, so that the non-aqueous secondary batteryaccording to this embodiment can be manufactured.

Alternatively, the non-aqueous secondary battery 100 may be manufacturedin the following way. A gel type electrolyte membrane is prepared inadvance by impregnating the electrolyte solution into a base materialformed of polymer. A layered structure stacking component is formedusing the sheet-like positive electrode 150, the sheet-like negativeelectrode 160, the electrolyte membrane, and the separator 170 asnecessary. Then, the stacking component is housed in the battery casing110.

The shape of the non-aqueous secondary battery 100 according to thisembodiment may include, for example, a cylindrical shape, an ellipticalshape, a square tube shape, a button shape, a coin shape, a flat shape,a laminate shape, or the like, without a particular limitation. Inparticular, according to this embodiment, the non-aqueous secondarybattery 100 preferably has a laminate shape.

Note that, in a case where the electrode arrangement is designed suchthat an outer edge of the negative-electrode active material layer andan outer edge of the positive-electrode active material layer areoverlapped with each other, or there is a portion where a width of thenon-facing part of the negative-electrode active material layer isexcessively small, a positional misalignment of the electrode may occurduring assembly of the battery, so that the charging/discharging cyclecharacteristic of the non-aqueous secondary battery may be degraded.Therefore, in the electrode body used in the non-aqueous secondarybattery, positions of the electrodes are preferably fixed in advanceusing a tape such as a polyimide tape, a polyphenylene sulfide tape, anda PP tape, an adhesive, or the like.

Although the non-aqueous secondary battery 100 according to thisembodiment can function as a battery through initial charging, it isstabilized as a part of the electrolyte solution is decomposed duringthe initial charging. Although there is no particular limitation in themethod of the initial charging, the initial charging is preferablyperformed to a capacity of 0.001 to 0.3 C, more preferably 0.002 to 0.25C, and furthermore preferably 0.003 to 0.2 C. It is also preferable thatthe initial charging is performed at a constant voltage on the way. Aconstant current for discharging a design capacity within one hour isset to “1 C”. By setting a voltage range in which lithium salt affectsan electrochemical reaction to be long, it is possible to achieve aneffect of suppressing an increase of internal resistance including thepositive electrode 150 by forming the SEI on the electrode surface, andany type of excellent effects to the positive electrode 150, theseparator 170, or the like other than the negative electrode 160,without strongly attaching a reaction product only to the negativeelectrode 160. For this reason, it is very effective to perform theinitial charging in consideration of the electrochemical reaction of thelithium salt dissolved in the non-aqueous electrolyte solution.

The non-aqueous secondary battery 100 according to this embodiment mayalso be used as a cell pack by connecting a plurality of non-aqueoussecondary batteries 100 in series or in parallel. From the viewpoint ofmanagement of the charging/discharging state of the cell pack, a workingvoltage range per non-aqueous secondary battery is preferably set to 2to 5 V, more preferably 2.5 to 5 V, and furthermore preferably 2.75 to 5V.

Next, preferable embodiments of the non-aqueous secondary battery willbe described.

Thirty First Embodiment: Non-Aqueous Secondary Battery

According to the thirty first embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous electrolyte solution containsacetonitrile and LiPO₂F₂. In addition, in the non-aqueous secondarybattery, a value obtained by dividing a bulk resistance at a temperatureof −30° C. in the measurement of electrochemical impedance spectroscopyby an internal resistance value is within a range of 0.05 to 0.7.

In the prior art, in order to guarantee reduction resistance of theacetonitrile electrolyte solution, it is necessary to form a strong filmformation agent. For this reason, an interface resistance significantlyincreases, and low-temperature performance is degraded,disadvantageously.

In the non-aqueous secondary battery according to the thirty firstembodiment, an acetonitrile electrolyte solution having a low meltingpoint and a high ionic conductivity is employed. Therefore, an increaseof the internal resistance caused by the electrolyte solution isinsignificant even under the −30° C. environment. In addition, sinceLiPO₂F₂ and cyclic acid anhydride are received by the film product, afilm having a low interface resistance even under a low temperature isprovided. Specifically, the non-aqueous electrolyte solution containsacetonitrile and lithium salt, and the value obtained by dividing a bulkresistance at a temperature of −30° C. in the measurement ofelectrochemical impedance spectroscopy by an internal resistance valueis within a range of 0.05 to 0.7.

Using the non-aqueous secondary battery according to the thirty firstembodiment, it is possible to perform evaluation in the measurement ofelectrochemical impedance spectroscopy under the −30° C. environment.

Note that the positive electrode active material may include lithiumcobaltate (LiCoO₂:LCO), a ternary system positive electrode materialLi(Ni/Co/Mn)O₂:NCM, or the like.

The non-aqueous electrolyte solution according to the thirty firstembodiment contains, for example, acetonitrile, LiPF₆, LiN(SO₂F)₂,LiN(SO₂CF₃)₂, and LiPO₂F₂. In addition, in the non-aqueous secondarybattery according to the thirty first embodiment, a material of theseparator having high porosity is preferably employed. There is noparticular limitation in the negative electrode and the battery casing.

The non-aqueous secondary battery according to the thirty firstembodiment is particularly suitable for applications in a cold region.

Thirty Second Embodiment: Non-Aqueous Secondary Battery

According to the thirty second embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains acompound containing at least one functional group selected from a groupconsisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—. In addition, in thenon-aqueous secondary battery, the value obtained by dividing a bulkresistance at a temperature of −30° C. in the measurement ofelectrochemical impedance spectroscopy by an internal resistance valueis within a range of 0.05 to 0.7.

According to the thirty second embodiment, the inventors achieved theinvention in view of a fact that the acetonitrile electrolytic solutiongenerates metal elution derived from the positive-electrode activematerial, and as a result, the interface resistance increases, so thatthe high-temperature performance and the low-temperature performancedecrease.

According to the thirty second embodiment, as described above, thenon-aqueous secondary battery contains a compound containing at leastone functional group selected from a group consisting of —N═, —NH₄,—N═O, —NH—NH—, and (NO₃)—. As a result, it is possible to suppress anincrease of the internal resistance. Specifically, the value obtained bydividing a bulk resistance at a temperature of −30° C. in themeasurement of electrochemical impedance spectroscopy by an internalresistance value is within a range of 0.05 to 0.7.

According to the thirty second embodiment, the compound having theaforementioned functional group is preferably contained on a surfaceportion of the positive electrode of the battery by approximately 0.5 to20 atomic % as an N-concentration obtained from a result of an XPSanalysis described below. As a result, it is possible to effectivelysuppress metal elution derived from the positive-electrode activematerial and suppress an increase of the interface resistance of thepositive electrode.

According to the thirty second embodiment, the compound having theaforementioned functional group is preferably contained on a surfaceportion of the positive electrode of the battery by approximately 0.5 to6.5 atomic % as an N-concentration obtained from a result of an XPSanalysis described below, and a thermal history of 40° C. or higher isgenerated in the event of initial charging. As a result, it is possibleto suppress metal elution derived from the positive-electrode activematerial and improve a cycle life and safety.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the thirty second embodiment preferably contains,for example, acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH,LiPO₂F₂, or 1-methyl-1H-benzotriazole (MBTA).

In this case, there is no particular limitation in the negativeelectrode. Meanwhile, although the positive electrode is notparticularly limited, the positive-electrode active material preferablyincludes a lithium-containing compound having layered rock salt typecrystals.

The non-aqueous secondary battery according to the thirty secondembodiment preferably employs any one of the non-aqueous electrolytesolutions of the first to thirties embodiments.

There is no particular limitation in the separator and the batterycasing.

The non-aqueous secondary battery according to the thirty secondembodiment is preferably applicable to in-vehicle applications.

Thirty Third Embodiment: Non-Aqueous Secondary Battery

According to the thirty third embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The negative-electrode active material layercontains at least one compound selected from a group consisting of imidesalt and (SO₄)²⁻. The imide salt is at least one selected from a groupconsisting of Li salt and onium salt. In the non-aqueous secondarybattery described above, the bulk resistance at a temperature of 25° C.in the measurement of electrochemical impedance spectroscopy is 0.025ohm or smaller.

As a result, acetonitrile durability improves because a decompositionproduct derived from the imide salt forms a film on thenegative-electrode active material layer. In addition, since the bulkresistance at a temperature of 25° C. is 0.025 ohm or smaller, it ispossible to provide high output power and high durability.

According to this embodiment, a film formed of LiPO₂F₂ and cyclic acidanhydride is preferably provided on a surface of the negative-electrodeactive material. As a result, it is possible to suppress a resistanceincrease in a low-temperature range.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the thirty third embodiment preferably contains,for example, acetonitrile, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, or LiPO₂F₂.

In this case, the negative electrode preferably has a film derived fromimide salt. Meanwhile, there is no particular limitation in the positiveelectrode, the separator, and the battery casing.

In the non-aqueous secondary battery according to the thirty thirdembodiment, any one of the non-aqueous electrolyte solutions of thefirst to thirtieth embodiments is preferably employed.

Thirty Fourth Embodiment: Non-Aqueous Secondary Battery

According to the thirty fourth embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains atleast one compound selected from a group consisting of organic acid,salt thereof, acid anhydride, and Li₂O. The organic acid includes atleast one selected from a group consisting of acetic acid, oxalic acid,and formic acid. In addition, the value obtained by dividing a bulkresistance at a temperature of −30° C. in the measurement ofelectrochemical impedance spectroscopy by an internal resistance valueis within a range of 0.05 to 0.7.

The acetonitrile-based electrolyte solution has a high ionicconductivity with excellent balance between viscosity and relativedielectric constant. However, the durability of the negative electrodeSEI is degraded. In this regard, if a large amount of film formationagent is added, the internal resistance increases, and the batteryperformance is degraded, disadvantageously. The inventors achieved thethirty fourth embodiment of the invention in view of the problems of theprior art described above.

According to the thirty fourth embodiment, the battery contains at leastone compound selected from a group consisting of organic acid (such asacetic acid, oxalic acid, and formic acid), salt thereof, acidanhydride, and Li₂O. As a result, it is possible to suppress an increaseof the internal resistance. Specifically, in the non-aqueous secondarybattery, the value obtained by dividing a bulk resistance at atemperature of −30° C. in the measurement of electrochemical impedancespectroscopy by an internal resistance value is within a range of 0.05to 0.7.

According to the thirty fourth embodiment, the surface portion of thenegative electrode of the battery contains at least one compoundselected from a group consisting of organic acid (such as acetic acid,oxalic acid, and formic acid), salt thereof, acid anhydride, and Li₂O asmuch as 1 to 35 atomic % as an O-concentration obtained from a result ofthe XPS analysis described below. As a result, it is possible to form anegative electrode SEI having an excellent ionic conductivity andsuppress an increase of the internal resistance of the battery using theacetonitrile electrolytic solution. Therefore, it is possible toeffectively improve the cycle performance.

According to the thirty fourth embodiment, the surface portion of thenegative electrode of the battery contains at least one compoundselected from a group consisting of organic acid (such as acetic acid,oxalic acid, and formic acid), salt thereof, acid anhydride, and Li₂O asmuch as 10 to 25 atomic % as an O-concentration obtained from a resultof the XPS analysis described below. As a result, it is possible to formthe SEI having high acetonitrile resistance and reduce the additionamount of vinylene carbonate (VC) in the acetonitrile electrolyticsolution. As a result, it is possible to suppress an increase of theinternal resistance and effectively improve the output powerperformance.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the thirty fourth embodiment preferably contains,for example, acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, orLiPO₂F₂. In addition, in the non-aqueous secondary battery according tothe thirty fourth embodiment, any one of the non-aqueous electrolytesolutions of the first to thirtieth embodiments is preferably employed.Furthermore, in the non-aqueous secondary battery, there is nolimitation in the positive electrode, the negative electrode, theseparator, and the battery casing.

The non-aqueous secondary battery according to the thirty fourthembodiment is suitable for applications in a cold region.

Thirty Fifth Embodiment: Non-Aqueous Secondary Battery

According to the thirty fifth embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains atleast one compound selected from a group consisting of imide salt and(SO₄)²⁻ in the negative-electrode active material layer, and the imidesalt is at least one selected from a group consisting of Li salt andonium salt. In the non-aqueous secondary battery, the bulk resistance ata temperature of −30° C. in the measurement of electrochemical impedancespectroscopy is 0.07 ohm or smaller.

As a result, a decomposition product derived from the imide salt forms afilm on the negative-electrode active material layer to provide a filmhaving a small interface resistance. In addition, since the bulkresistance at a temperature of −30° is equal to or smaller than 0.07ohm, it is possible to provide a secondary battery having excellentbalance between the diffusion reaction and the interface reaction of thelithium ions and high low-temperature performance.

According to this embodiment, it is preferable that a film formed ofLiPO₂F₂ and cyclic acid anhydride is provided on a surface of thenegative-electrode active material. As a result, it is possible tosuppress a resistance increase in a low-temperature range.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the thirty fifth embodiment preferably contains,for example, acetonitrile, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, or LiPO₂F₂.

In this case, the negative electrode preferably has a film derived fromimide salt. Meanwhile, there is no particular limitation in the positiveelectrode, the separator, and the battery casing.

In the non-aqueous secondary battery according to the thirty fifthembodiment, any one of the non-aqueous electrolyte solutions of thefirst to thirtieth embodiments is preferably employed.

Thirty Sixth Embodiment: Non-Aqueous Secondary Battery

According to the thirty sixth embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains acompound containing at least one functional group selected from a groupconsisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—. In addition, thenon-aqueous secondary battery has a capacity retention rate of 70% orhigher, where the capacity retention rate is calculated by dividing the5 C discharge capacity by the 1 C discharge capacity after performing astorage test for 4 hours at a temperature of 85° C.

According to the thirty sixth embodiment, as described above, thenon-aqueous secondary battery contains a compound containing at leastone functional group selected from a group consisting of —N═, —NH₄,—N═O, —NH—NH—, and (NO₃)—. As a result, it is possible to suppress anincrease of the internal resistance. Specifically, the non-aqueoussecondary battery has a capacity retention rate of 70% or higher, wherethe capacity retention rate is calculated by dividing the 5 C dischargecapacity by the 1 C discharge capacity. In this manner, using thenon-aqueous secondary battery according to the thirty sixth embodiment,it is possible to obtain an excellent rate characteristic.

According to the thirty sixth embodiment, it is preferable that thenon-aqueous electrolyte solution contains a nitrogen-containingcompound, and the aging is performed at a voltage of 3.5 V or lowerduring initial charging. Before ionization of the transition metalderived from the positive-electrode active material, the compoundcontaining at least one functional group selected from a groupconsisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)— protects the surfaceof the positive electrode. As a result, it is possible to suppress anincrease of internal resistance over time caused by a thermal history.

According to the thirty sixth embodiment, the aging temperature ispreferably set to 35° C. or higher and 60° C. or lower. By applying athermal history at a temperature lower than 60° C., the protective filmcan inactivate the activation point of the positive electrode surface atan early stage and suppress an increase of internal resistance under ahigh temperature condition.

The non-aqueous secondary battery according to the thirty sixthembodiment includes a positive electrode having a positive-electrodeactive material layer formed on one or both sides of a currentcollector, a negative electrode having a negative-electrode activematerial layer formed on one or both sides of a current collector, and anon-aqueous electrolyte solution.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the thirty sixth embodiment preferably contains,for example, acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH,LiPO₂F₂, or 1-methyl-1H-benzotriazole (MBTA). In addition, in thenon-aqueous secondary battery according to the thirty sixth embodiment,any one of the non-aqueous electrolyte solutions of the first tothirtieth embodiments is preferably employed. In this case, in thenon-aqueous secondary battery, there is no particular limitation in thenegative electrode, the positive electrode, the separator, and thebattery casing.

The thirty sixth embodiment is preferably applicable to a power toolrequiring a high rate characteristic with high performance and highoutput power.

Thirty Seventh Embodiment: Non-Aqueous Secondary Battery

According to the thirty seventh embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains atleast one compound selected from a group consisting of organic acid,salt thereof, acid anhydride, and Li₂O. In this case, the organic acidincludes at least one selected from a group consisting of acetic acid,oxalic acid, and formic acid. In addition, the non-aqueous secondarybattery has a capacity retention rate of 70% or higher, where thecapacity retention rate is calculated by dividing the 5 C dischargecapacity by the 1 C discharge capacity after performing a storage testof 4 hours at a temperature of 85° C.

If the non-aqueous secondary battery is applied to a power toolrequiring a high rate characteristic with high performance and highoutput power, the rate characteristic is reduced as a service timeincreases because a thermal history of the electrolyte solution isinevitable in this application. In view of such a problem, the inventionof the thirty seventh embodiment has been achieved.

According to the thirty seventh embodiment, it is possible to suppressan increase of internal resistance and resist to the thermal history bycontrolling an aging condition during initial charging.

According to the thirty seventh embodiment, the non-aqueous electrolytesolution contains cyclic acid anhydride, and aging is performed at avoltage of 3.5 V or lower during initial charging. According to thirtyseventh embodiment, the negative electrode SEI film contains at leastone compound selected from a group consisting of organic acid (such asacetic acid, oxalic acid, and formic acid), salt thereof, acidanhydride, and Li₂O. Therefore, it is possible to suppress an increaseof internal resistance over time caused by a thermal history.

According to the thirty seventh embodiment, the aging temperature ispreferably set to 35° C. or higher and 60° C. or lower. As a result, itis possible to appropriately suppress thermal decomposition of LiPF₆that may occur at a temperature of 60° C. or higher.

The non-aqueous electrolyte solution according to the thirty seventhembodiment preferably contains, for example, acetonitrile, LiPF₆,LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, 1-methyl-1H-benzotriazole(MBTA). In the non-aqueous secondary battery according to the thirtyseventh embodiment, any one of the non-aqueous electrolyte solutions ofthe first to thirtieth embodiments is preferably employed. In this case,there is no particular limitation in the negative electrode, thepositive electrode, the separator, and the battery casing.

The thirty seventh embodiment is preferably applicable to a power toolrequiring a high rate characteristic with high performance and highoutput power.

Thirty Eighth Embodiment: Non-Aqueous Secondary Battery

According to the thirty eighth embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains acompound containing at least one functional group selected from a groupconsisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—. In addition, thenon-aqueous secondary battery has a 0° C. ionic conductivity of 10 mS/cmor higher after performing a storage test for 4 hours at a temperatureof 85° C.

In this manner, in the non-aqueous secondary battery according to thethirty eighth embodiment, it is possible to increase the 0° C. ionicconductivity measured so as to expose the battery to a heat of 85° C.while being charged with 4.2 V and then decreasing the temperature to 0°C., compared to the prior art. In this manner, it is possible toincrease resistance to the thermal history. Therefore, it is possible tomaintain a high ionic conductivity even when the battery is carried froma high-temperature environment to a low temperature environment.Therefore, even when the battery is used in an application where thethermal history is severe, it is possible to achieve excellentlow-temperature characteristics. According to this embodiment, it ispossible to operate the battery even at a temperature lower than alimitation temperature of the operation range of the existingelectrolyte solution.

According to the thirty eighth embodiment, it is possible to suppress adecomposition product of the nitrogen-containing compound by defining amixing sequence of the non-aqueous electrolyte solution. The non-aqueouselectrolyte solution effectively functions as a protection filmformation agent of the positive electrode.

According to the thirty eighth embodiment, a non-aqueous electrolytesolution containing acetonitrile and the nitrogen-containing compound isemployed. As a result, it is possible to appropriately form the positiveelectrode protection film and suppress generation of HF that causes anincrease of the internal resistance.

According to the thirty eighth embodiment, a temperature increase at thetime of adding the nitrogen-containing compound is preferably suppressedto 50° C. or lower. As a result, it is possible to appropriatelysuppress thermal decomposition of the nitrogen-containing compoundgenerated at a temperature of 60° C. or higher.

The non-aqueous electrolyte solution according to the thirty eighthembodiment preferably contains acetonitrile, LiPF₆, LiN(SO₂F)₂,LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, 1-methyl-1H-benzotriazole (MBTA). Inaddition, the non-aqueous electrolyte solution according to any one ofthe first to thirtieth embodiments is preferably employed in thenon-aqueous secondary battery according to the thirty eighth embodiment.In this case, there is no particular limitation in the negativeelectrode, the positive electrode, the separator, and the batterycasing.

The non-aqueous secondary battery according to the thirty eighthembodiment is suitable for use as an in-vehicle storage batterycompatible with a cold region.

Thirty Ninth Embodiment: Non-Aqueous Secondary Battery

According to the thirty ninth embodiment, the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution. The non-aqueous secondary battery contains atleast one compound selected from a group consisting of organic acid,salt thereof, acid anhydride, and Li₂O. In addition, the organic acidincludes at least one selected from a group consisting of acetic acid,oxalic acid, and formic acid. In addition, the non-aqueous secondarybattery has a 0° C. ionic conductivity of 10 mS/cm or higher afterperforming a storage test for 4 hours at a temperature of 85° C.

The low-temperature characteristic of the non-aqueous secondary batteryis disadvantageously degraded as a service time increases in anapplication where a thermal history of the non-aqueous electrolytesolution is inevitable.

According to the thirty ninth embodiment, it is preferable to determinea mixing sequence of the non-aqueous electrolyte solution. As a result,it is possible to suppress a decomposition product of LiPF₆ and improveresistance to the thermal history. According to the thirty ninthembodiment, it is preferable to obtain the non-aqueous electrolytesolution by adding acetonitrile and cyclic acid anhydride and thenadding LiPF₆. As a result, it is possible to suppress an abrupttemperature increase when adding LiPF₆ and suppress generation of HFthat may increase the internal resistance due to a sacrificial reactionof the cyclic acid anhydride.

According to the thirty ninth embodiment, it is preferable to suppress atemperature increase caused by adding LiPF₆ to 50° C. or lower. As aresult, it is possible to suppress thermal decomposition of LiPF₆ thatmay occur at a temperature of 60° C. or higher.

The non-aqueous electrolyte solution according to the thirty ninthembodiment preferably contains, for example, acetonitrile, LiPF₆,LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, or 1-methyl-1H-benzotriazole(MBTA). In addition, the non-aqueous electrolyte solution according toany one of the first to thirtieth embodiments is preferably employed inthe non-aqueous secondary battery according to the thirty ninthembodiment. In this case, there is no particular limitation in thenegative electrode, the positive electrode, the separator, and thebattery casing.

The non-aqueous secondary battery according to the thirty ninthembodiment is preferably applicable to an in-vehicle battery.

Fortieth Embodiment: Non-Aqueous Secondary Battery

According to the fortieth embodiment, in the non-aqueous secondarybattery of any one of the thirty first to thirty ninth embodiments, thepositive-electrode active material preferably contains alithium-containing composite metal oxide expressed as “Li_(z)MO₂” where“M” denotes at least one metal element selected from a group consistingof Ni, Mn, Co, Al, and Mg, the content of Ni is more than 50%, and “z”denotes a number greater than 0.9 and smaller than 1.2, from theviewpoint of increasing the energy density of the non-aqueous secondarybattery.

According to this embodiment, using the electrolyte solution containingacetonitrile and a nitrogen-containing compound, it is possible tosuppress capacity degradation caused by an unstable crystal structureeven when the nickel content increases.

According to this embodiment, it is preferable that the charging voltageis 4.3 V or higher in the non-aqueous secondary battery obtained byusing the high nickel positive electrode as the positive-electrodeactive material. As a result, it is possible to set the design capacityto 150 Ah/L or larger.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the fortieth embodiment preferably contains, forexample, acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, or1-methyl-1H-benzotriazole (MBTA). In addition, the non-aqueouselectrolyte solution according to any one of the first to thirtiethembodiments is preferably employed in the non-aqueous secondary batteryaccording to the fortieth embodiment. In this case, there is noparticular limitation in the negative electrode, the positive electrode,the separator, and the battery casing.

Forty First Embodiment: Non-Aqueous Secondary Battery

According to the forty first embodiment, in the non-aqueous secondarybattery of the thirty first to fortieth embodiments, an electricpotential difference of the negative electrode around injection of thenon-aqueous electrolyte solution is preferably 0.3 V or higher.

According to the forty first embodiment, the invention has been made inview of a fact that a metal having a high standard electrode potentialis eluted, and safety is degraded if the battery is stored for a longtime without performing a charging/discharging test after injection ofthe electrolyte solution. Here, the standard electrode potential is anelectric potential expressed with respect to an electric potential (0 V)of a standard hydrogen electrode.

According to the forty first embodiment, a non-aqueous electrolytesolution containing acetonitrile and lithium salt is employed as thenon-aqueous electrolyte solution. According to the forty firstembodiment, the negative electrode electric potential of the batteryafter liquid injection can be lowered to the vicinity of 2.6 V vs.Li/Li⁺. As a result, it is possible to avoid an electric potential atwhich the copper current collector is eluted. In the non-aqueoussecondary battery known in the prior art, no electric potentialdifference is generated as long as electricity does not flow. However,in the non-aqueous secondary battery according to this embodiment, anelectric potential difference is generated after liquid injection evenbefore electricity conduction, which is very unique. This electricpotential difference is presumed as a spontaneous lithium ion insertionreaction to the negative electrode caused by a high ionic conductivity,and is expected to contribute to formation of a dense SEI.

According to the forty first embodiment, the negative electrode containsat least one of metals having a standard electrode potential of 0 V orhigher. Since the negative electrode using the existing carbonateelectrolyte solution has an electric potential close to 3.1 V vs. Li/Li⁺after liquid injection, elution of a metal element having a highstandard electrode potential gradually proceeds as it is stored for along time. Meanwhile, the electrolyte solution using acetonitrile doesnot cause elution even when it is stored for a long time after liquidinjection. Therefore, it is possible to extend a manufacturing controlperiod including the impregnation time.

According to the forty first embodiment, the negative electrode currentcollector is preferably formed of copper. As a result, it is possible tosuppress elution of copper without generating a charging/discharginghistory.

The non-aqueous electrolyte solution used in the non-aqueous secondarybattery according to the forty first embodiment preferably contains, forexample, acetonitrile, LiPF₆, LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, or1-methyl-1H-benzotriazole (MBTA). In addition, the non-aqueouselectrolyte solution according to any one of the first to thirtiethembodiments is preferably employed in the non-aqueous secondary batteryaccording to the forty first embodiment. In this case, the negativeelectrode preferably has a current collector using metal having astandard electrode potential of 0 V or higher. Meanwhile, there is noparticular limitation in the positive electrode, the separator, and thebattery casing.

Forty Second Embodiment: Non-Aqueous Secondary Battery

According to the forty second embodiment, in the non-aqueous secondarybattery of any one of the thirty first to forty first embodiments, a gasgeneration amount in a storage test for 200 hours at 60° C. ispreferably 0.008 ml or smaller per 1 mAh.

Since acetonitrile promotes reductive decomposition at a hightemperature, a large amount of gas is generated when it is stored at ahigh temperature for a long time. According to the forty secondembodiment, the non-aqueous electrolyte solution preferably containsacetonitrile, LiPO₂F₂, acetic acid, and cyclic acid anhydride. As aresult, LiPO₂F₂, acetic acid, and cyclic acid anhydride function asreduction resistance, and acetonitrile is reductively decomposed, sothat it is possible to suppress gas generation.

According to the forty second embodiment, the non-aqueous secondarybattery is preferably a pouch type non-aqueous secondary batterycontaining acetonitrile, LiPO₂F₂, acetic acid, and cyclic acidanhydride. Due to the LiPO₂F₂, acetic acid, and cyclic acid anhydride,the SEI is formed on the surface of the negative electrode, and it ispossible to suppress reduction of acetonitrile from being promoted at ahigh temperature.

According to the forty second embodiment, the content of acetic acid ispreferably set to 0.1 ppm or more and 5 ppm or less with respect to thenon-aqueous electrolyte solution. As a result, it is possible to moreeffectively set the gas generation amount in the storage test for 200hours at 60° C. to 0.008 ml or less per 1 mAh.

The non-aqueous electrolyte solution according to the forty secondembodiment preferably contains acetonitrile, LiN(SO₂F)₂, LiN(SO₂CF₃)₂,LiPO₂F₂, and acetic acid. In addition, the non-aqueous electrolytesolution of any one of the first to thirtieth embodiments is preferablyemployed in the non-aqueous secondary battery according to the fortysecond embodiment. In this case, there is no particular limitation inthe negative electrode, the positive electrode, the separator, and thebattery casing.

Forty Third Embodiment: Non-Aqueous Secondary Battery

According to the forty third embodiment, in the non-aqueous secondarybattery of the thirty first to forty second embodiments, a resistanceincrease rate in a full-charge storage test for 720 hours at 60° C. ispreferably 400% or lower.

According to the forty third embodiment, the invention has been achievedin view of a problem that, in the non-aqueous electrolyte solutioncontaining acetonitrile and LiPF₆, acetonitrile and LiPF₆ react and areviolently decomposed at a high temperature, and a resistance increaserate of the internal resistance significantly increases.

The forty third embodiment is suitable for a storage battery using thenon-aqueous secondary battery containing acetonitrile, compatible with acold region. According to the forty third embodiment, it is possible tosuppress an increase of internal resistance during high-temperatureheating and obtain excellent low-temperature characteristics.

According to the forty third embodiment, it is preferable that thesolvent of the electrolyte solution containing imide salt containsacetonitrile, and the non-aqueous secondary battery is a storage batterycontaining LiPO₂F₂ and cyclic acid anhydride as the additive andcompatible with a cold region. As a result, it is possible to suppressan increase of internal resistance during high-temperature heating andobtain excellent low-temperature characteristics.

According to the forty third embodiment, imide salt is preferablycontained in a molarity relationship of “LiPF₆≤imide salt”. Therefore,it is possible to suppress reduction of the ionic conductivity at a lowtemperature and obtain excellent low-temperature characteristics. TheLiPO₂F₂ and cyclic acid anhydride suppress an increase of the internalresistance during high-temperature heating. In addition, the imide saltcontributes to improvement of the low-temperature characteristics.

According to the forty third embodiment, a non-aqueous electrolytesolution containing acetonitrile and at least one selected from a groupconsisting of succinic anhydride, maleic anhydride, and phthalicanhydride is preferably employed. As a result, it is possible tosuppress an increase of the internal resistance during high-temperatureheating and obtain excellent low-temperature characteristics.

The non-aqueous electrolyte solution according to the forty thirdembodiment preferably contains for example, acetonitrile, LiPF₆,LiN(SO₂F)₂, LiN(SO₂CF₃)₂, SAH, LiPO₂F₂, and 1-methyl-1H-benzotriazole(MBTA). In addition, the non-aqueous electrolyte solution of any one ofthe first to thirtieth embodiments is preferably employed in thenon-aqueous secondary battery according to the forty third embodiment.In this case, there is no particular limitation in the negativeelectrode, the positive electrode, the separator, and the batterycasing.

Forty Fourth Embodiment: Cell Pack

A cell pack according to the forty fourth embodiment has the non-aqueoussecondary battery of any one of the thirty first to forty thirdembodiments.

The non-aqueous secondary battery of any one of the thirty first toforty third embodiments has a positive-electrode active material layercontaining a lithium-containing compound containing Fe. In addition, thenegative-electrode active material layer contains graphite or at leastone element selected from a group consisting of Ti, V, Sn, Cr, Mn, Fe,Co, Ni, Zn, Al, Si, and B.

The non-aqueous electrolyte solution contains cyclic carbonate withoutsaturated secondary carbon, and the cyclic carbonate without saturatedsecondary carbon includes at least one selected from a group consistingof ethylene carbonate and vinylene carbonate.

According to the forty fourth embodiment, the non-aqueous secondarybattery is configured by using a single module or connecting two or moremodules in parallel, in which the module is obtained by connecting fourcells in series, or by connecting four modules in series, in which themodule is formed by connecting two or more cells in parallel. Inaddition, an operation voltage range per cell is within a range of 1.8to 3.7 V, and an average operation voltage is set to 2.5 to 3.5 V. Inaddition, each module is mounted with a battery management system (BMS)for diagnosing a battery charge state and an operation state.

In a case where an electrolyte solution containing acetonitrile as amain solvent is used as the lithium ion battery, reductive decompositionproceeds at a negative electrode electric potential of graphite.Therefore, a negative electrode capable of absorbing lithium ions at 0.4V (vs. Li/Li⁺) or higher has been used. However, according to the fortyfourth embodiment, since the electrolyte solution containing ethylenecarbonate or vinylene carbonate and the positive electrode of ironphosphate lithium (LiFePO₄:LFP) and/or the negative electrode ofgraphite are employed, it is possible to improve a cycle life at a hightemperature. The LFP has excellent high-temperature characteristics,compared to other positive electrode materials such as lithium cobaltate(LiCoO₂:LCO) or a ternary system positive electrode material(Li(Ni/Co/Mn)O₂:NCM). In addition, in a case where an electrolytesolution containing acetonitrile as a main solvent is employed as thelithium ion battery, reductive decomposition proceeds at the negativeelectrode electric potential of graphite. Therefore, a negativeelectrode capable of absorbing lithium ions at 0.4 V (vs Li/Li⁺) orhigher is employed. In addition, ethylene carbonate or vinylenecarbonate is reductively decomposed on the graphite negative electrode,so as to form a film having excellent high-temperature durability.

According to the forty fourth embodiment, since the operation voltagerange per cell is set within a range of 1.8 to 3.7 V, it is possible tosubstitute an existing four-series 12V lead acid battery. Since aspecification of an electric system is defined on the basis of theoperation voltage range of the lead acid battery, it is very importantto determine the operation voltage range per cell. For this reason, itis preferable to mount the BMS for appropriately managing the voltage.

According to the forty fourth embodiment, the cell preferably contains anon-aqueous electrolyte solution having an −30° C. ionic conductivity of3 mS/cm or higher. As a result, it is possible to obtain both thehigh-temperature durability and the low-temperature performance.

The cell pack according to the forty fourth embodiment is suitable for amobile entity application or a stationary application. The mobile entityapplication includes a hybrid electric vehicle (HEV), a fork lift, agolf cart, an e-motorcycle, an automated guided vehicle (AGV), a train,a ship, or the like. In addition, the stationary application includes anuninterruptible power supply (UPS) device, an emergency power system, anenergy storage system, or the like.

Forty Fifth Embodiment: Hybrid Power System

A hybrid power system according to the forty fifth embodiment includesthe cell pack of the forty fourth embodiment, and a module having asecondary battery other than the lithium ion battery or a cell pack incombination.

In this embodiment, a power system is configured by connecting a moduleand a second secondary battery in parallel, so that energy generated inbraking of a traveling vehicle can be efficiently used as regenerativeenergy by supplementing a lithium ion battery (LIB) capable of receivinga large current with the current flowing through the battery that is notcapable of receiving a large current in the event of charging caused bybraking of vehicle deceleration or the like. The second secondarybattery may include, for example, a lead acid battery, a nickel hydrogenbattery, a Ni—Cd battery, an electric double layer capacitor (EDLC), alithium ion capacitor (LIC), or the like. In addition, the secondsecondary battery may include a next-generation battery or an innovationbattery such as an all-solid battery, a lithium-sulfur battery, alithium-air battery, a sodium ion battery, a multivalent ion batterybased on magnesium ions or calcium ions, or the like. Note that thesecondary battery other than the lithium ion battery according to thisembodiment is not limited thereto. A power system combined with agenerative energy device such as a fuel cell battery or a solar cellbattery may also be employed.

According to the forty fourth embodiment, the hybrid power system ispreferably a combinational hybrid power system in which the LIB moduleof the forty fourth embodiment and the secondary battery other than thelead acid battery are combined. Here, the module is formed by connectinga plurality of cells, and the cell pack is formed by connecting aplurality of modules. However, the cell pack is a terminology includingthe module. In the LIB of the prior art, an organic solvent is used inthe electrolyte solution. Therefore, viscosity of the electrolytesolution increases at a low temperature, and the internal resistancesignificantly increases. As a result, the low-temperature output powerof the LIB is reduced, compared to the lead acid battery. Meanwhile, thelead acid battery has low output power at 25° C. but has high outputpower at −10° C.

In this regard, according to the forty fifth embodiment, a 12V vehiclepower system is configured by connecting the LIB module of the fortyfourth embodiment to the secondary battery other than the lead acidbattery in parallel, and a large current is supplemented to the LIBmodule of the forty fourth embodiment capable of receiving a largecurrent in the event of charging caused by braking of vehicledeceleration or the like. As a result, it is possible to efficiently useenergy generated in the event of braking of a traveling vehicle such asan automobile as regenerative energy.

According to the forty fifth embodiment, iron phosphate lithium(LiFePO₄) is used as the positive-electrode active material of the LIB,and graphite is used as the negative-electrode active material, so thatthe electrolyte solution preferably has a 20° C. ionic conductivity of18 mS/cm or higher. Since iron phosphate lithium has a lower electronconductivity, compared to NCM or LCO, it has a problem incharging/discharging. For this reason, its advantage may be degradedwhen it is combined with a secondary battery other than the LIB. In thisregard, by using an electrolyte solution having a high ionicconductivity, it is possible to cope with a wide temperature range froma low temperature to a room temperature in the large-currentcharging/discharging. Therefore, it is possible to extend a servicelife.

Forty Sixth Embodiment: Cell Pack

A cell pack according to the forty sixth embodiment has the non-aqueoussecondary battery of any one of the thirty first to forty thirdembodiments.

The non-aqueous secondary battery of any one of the thirty first toforty third embodiments has a positive-electrode active material layercontaining a lithium-containing compound containing Fe. In addition, thenegative-electrode active material layer contains graphite or at leastone element selected from a group consisting of Ti, V, Sn, Cr, Mn, Fe,Co, Ni, Zn, Al, Si, and B.

The non-aqueous electrolyte solution contains cyclic carbonate withoutsaturated secondary carbon, and the cyclic carbonate without saturatedsecondary carbon includes at least one selected from a group consistingof ethylene carbonate and vinylene carbonate.

The non-aqueous secondary battery is configured by the single cell packor by connecting two or more cell packs in parallel on the basis of thefollowing formulas (2) and (3) that define the number of cells and thenumber of modules of the non-aqueous secondary battery. Alternatively,the cell pack is configured by connecting modules in which two or morecells are connected in parallel, on the basis of the formulas (2) and(3).Number of cells connected in series per module (X): X=2,4,8, or16  Formula (2)Number of modules connected in series per cell pack (Y): Y=16/X  Formula(3)

The operation voltage range per cell is within a range of 1.8 to 3.7 V,the average operation voltage is 2.5 to 3.5 V, and the module is mountedwith the BMS. Here, the average operation voltage refers to a voltagewhen a percentage of the charged electricity amount relative to anelectric capacity (state of charge: SOC) is at 50%.

The LFP electrode has a poor electron conductivity, low current emissionand acceptance performance, compared to NCM or LCO. Since the in-vehiclebattery has an electronic device requiring a large current, the LFP isdifficult to apply disadvantageously. However, according to the fortysixth embodiment, since the electrolyte solution containing ethylenecarbonate or vinylene carbonate, the LFP positive electrode and/or thegraphite negative electrode are employed, it is possible to improve acycle life at a high temperature. The LFP has excellent high-temperaturecharacteristics, compared to the positive electrode material such as NCMor LCO. In addition, ethylene carbonate or vinylene carbonate isreductively decomposed on the graphite negative electrode, so as to forma film having excellent high-temperature durability.

According to this embodiment, the operation voltage range per cell ispreferably within a range of 1.8 to 3.7 V, and the average operationvoltage is preferably 2.5 to 3.5 V. In addition, the BMS is preferablymounted on a module or a system, and the cell pack is preferablyconfigured by connecting one or more modules connected in series inparallel. Alternatively, in the non-aqueous secondary battery of any oneof the thirty first to forty third embodiments, the cell pack ispreferably configured by forming a module by connecting two or morecells in parallel and connecting fourteen to sixteen modules in series.In this manner, by setting the operation voltage range per cell to 1.8to 3.7 V, the non-aqueous secondary battery can be connected to electricequipment complying with a 48V power standard LV148 (defined in 2011) byconnecting sixteen modules in series.

According to the forty sixth embodiment, the cell preferably includes anelectrolyte solution containing acetonitrile as a solvent, a separatorhaving high porosity, a member obtained by coating a surface of thepositive-electrode active material particle with carbon, a positiveelectrode mixture layer containing a conductive aid of 5 mass % or more,and a member obtained by coating a surface of a positive electrodecharge collecting foil with carbon. In this manner, for the ionicconduction portion, acetonitrile having a high ionic conductivity isadded to the electrolyte solution, and a nonwoven fabric having highporosity is used. In addition, for the electron movement portion, aconduction path from the charge collecting foil to a gap betweenparticles is improved using each member. As a result, it is possible toachieve high output power performance.

The cell pack according to the forty sixth embodiment is suitable for amobile entity application or a stationary application. The mobile entityapplication includes a hybrid electric vehicle (HEV), a fork lift, agolf cart, an e-motorcycle, an automated guided vehicle (AGV), a train,a ship, or the like. In addition, the stationary application includes anuninterruptible power supply (UPS) device, an emergency power system, oran energy storage system.

Forty Seventh Embodiment: Hybrid Power System

A hybrid power system according to the forty seventh embodiment includesthe cell pack of the forty sixth embodiment, and a module or a cell packhaving a secondary battery other than the lithium ion battery incombination.

As a result, a 48V power system and a 12V power system are provided incombination, so that, even when one of them is shut down, the othersystem can supplement it.

According to the forty seventh embodiment, it is preferable that the LIBmodule of the forty second embodiment and a lead acid battery arecombined as a combinational system. As a result, the 48V power systemcorresponds to the LIB, and the 12V power system corresponds to thebattery other than LIB, so that it is possible to obtain a power systemhaving excellent balance between the energy density and the system cost.

According to the forty seventh embodiment, it is preferable that thepositive-electrode active material of the LIB is iron phosphate lithium(LiFePO₄), the negative-electrode active material of the LIB isgraphite, and the electrolyte solution has an 20° C. ionic conductivityof 15 mS/cm or higher. Since the iron phosphate lithium has a lowerelectron conductivity, compared to NCM or LCO, there may be a problem incharging/discharging, and advantages may be degraded when it is combinedwith the lead acid battery. Therefore, by using the electrolyte solutionhaving a high ionic conductivity, it is possible to cope withlarge-current charging/discharging of the lead acid battery in thevicinity of the room temperature and extend the service life untilreplacement of the battery.

While embodiments of the invention have been described hereinbefore, theinvention is not limited by the aforementioned embodiments. Variouschanges or modifications may be possible without departing from thespirit and scope of the invention.

EXAMPLES

In the following examples and comparative examples, Lithium BatteryGrade produced by Kishida Chemical Co., Ltd. was employed asacetonitrile.

Examples of the first to seventh embodiments will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 1. Note that, in Table 1, “AcN” denotes acetonitrile,“DEC” denotes diethyl carbonate, “DMC” denotes dimethyl carbonate, “EMC”denotes ethyl methyl carbonate, “EC” denotes ethylene carbonate, “VC”denotes vinylene carbonate, “PC” denotes propylene carbonate, “LiPF₆”denotes lithium hexafluorophosphate, “LiBOB” denotes lithiumbis(oxalate) borate, “LiN(SO₂F)₂” denotes lithium bis (fluorosulfonyl)imide, “LiN(SO₂CF₃)₂” denotes lithium bis (trifluoromethane sulfonyl)imide, “SAH” denotes succinic anhydride, “MAH” denotes maleic anhydride,“PAH” denotes phthalic anhydride, and “LiPO₂F₂” denotes lithiumdifluorophosphate.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 1 Lithium salt Solvent Imide salt Additive AcN DEC DMC EMC LiPF₆LiBOB Content Cyclic acid (vol (vol (vol (vol EC VC PC (mol/1 L (mol/1 L(mol/1 L anhydride LiPO₂F₂ %) %) %) %) (vol %) (vol %) (vol %) solvent)solvent) Type solvent) (mass %) (mass %) Example 1 40 0 0 35 17 8 0 0.250 LiN(SO₂F)₂ 1.75 SAH 0.2 0.1 Example 2 38 35 0 0 0 6 21 0.6 0LiN(SO₂CF₃)₂ 0.3 MAH 0.15 0.5 Example 3 65 0 6 0 22 7 0 0.6 0LiN(SO₂CF₃)₂ 0.6 PAH 0.5 0.05 Comparative 47 42 0 0 0 11 0 1.3 0.1 — —MAH 0.07 — Example 1 Comparative 20 0 0 42 21 17 0 1 0 — — — 0.0005Example 2

<Lithium Foil Immersion Test>

A metal lithium foil having a thickness of 200 μm with a size of 5 mm by5 mm was immersed into each electrolyte solution of 5 mL prepared asdescribed above, and it was stored for a day (24 hours) at a temperatureof 60° C. After storing for a day (24 hours), the state of the metallithium foil immersed in each electrolyte solution was observed andevaluated on the basis of the following standard. If deformation of themetal lithium foil is recognized, a mark “x” was given. If theelectrolyte solution is transparent without any color, and the metallithium foil is not deformed, a mark “o” was given.

Examples and Comparative Examples

For the examples and the comparative examples, an electrolyte solutionwas produced using the composition of Table 1, and the metal lithiumfoil was immersed using the aforementioned method. Then, it was storedfor a day (24 hours) at a temperature of 60° C. After storing for a day(24 hours), the evaluation was performed on the basis of theaforementioned criteria. The result is shown in Table 2.

TABLE 2 Lithium foil immersion test (60° C., 24 hours) Example 1 ∘Example 2 ∘ Example 3 ∘ Comparative Example 1 x Comparative Example 2 x

In Examples 1 to 3, discoloration of the non-aqueous electrolytesolution or deformation of the metal lithium foil were not observed. Incomparison, in Comparative Examples 1 and 2, discoloration of thenon-aqueous electrolyte solution or deformation of the metal lithiumfoil were observed. In Examples 1 to 3, it was recognized that thenon-aqueous electrolyte solution contains acetonitrile of thenon-aqueous solvent, lithium salt, LiPO₂F₂, and cyclic acid anhydride.Meanwhile, in the comparative examples, the non-aqueous electrolytesolution does not contain any one of LiPO₂F₂ and cyclic acid anhydride.As a result, it was recognized that, in the electrolyte solutioncontaining acetonitrile, LiPO₂F₂ and cyclic acid anhydride act toreduction resistance. That is, it was recognized that, due to LiPO₂F₂and cyclic acid anhydride, the SEI is formed on the surface of the metallithium foil. As a result, it was recognized that, in a case where theelectrolyte solution containing LiPO₂F₂ and cyclic acid anhydride isused in the non-aqueous secondary battery, the SEI can be formed on thenegative electrode. For this reason, it is possible to suppressreduction of the electrolyte solution from being promoted at a hightemperature, and suppress generation of gas caused by reductivedecomposition of the electrolyte solution.

If LiPO₂F₂ and cyclic acid anhydride are contained in the electrolytesolution, the SEI formed on the negative electrode is reinforced. Forthis reason, when acetonitrile is contained as the non-aqueous solvent,the SEI of the negative electrode is not easily dissolved even under ahigh-temperature environment, so that it is possible to suppressreductive decomposition of acetonitrile.

Therefore, the lower limit of LiPO₂F₂ was set to 0.001 mass % or more,excluding Comparative Example 2, and the upper limit was set to 1 mass %or less on the basis of Example 2. In addition, the lower limit of thecyclic acid anhydride was set to 0.01 mass % or more, and the upperlimit was set to 1 mass % or less on the basis of Example 3. Byadjusting the contents of LiPO₂F₂ and cyclic anhydride, the SEI isfurther reinforced.

On the basis of the experimental results of the examples and thecomparative examples, it was preferable that PO₂F₂ anions of 0.001 to 1mass % and cyclic acid anhydride of 0.01 to 1 mass % are added to theelectrolyte solution, and the cyclic acid anhydride includes at leastone selected from a group consisting of succinic anhydride (SAH), maleicanhydride (MAH), and phthalic anhydride (PAH).

As a result, it was recognized that the SEI is appropriately formed. Inaddition, the SEI is further reinforced by further adjusting thecontents of LiPO₂F₂ and cyclic acid anhydride.

From the experimental result of Example 1, it was preferable that theelectrolyte solution contains acetonitrile, and the cyclic acidanhydride includes succinic anhydride.

Examples of the eighth and ninth embodiments will now be described.

<Manufacturing of Non-Aqueous Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture. N-methyl-2-pyrrolidone as a solvent wasadded to the obtained positive electrode mixture until a solid contentof 68 mass %, and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 11.5 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,so that a positive electrode having the positive-electrode activematerial layer and the positive electrode current collector wasobtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 6.9 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.30 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

The multi-layered laminate-type battery has a design capacity value ofapproximately 10 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,a battery was manufactured using the method described in the chapter(1-1) to (1-3), and evaluation was performed in the sequence of thechapters (2-1) and (2-2). Finally, the ionic conductivity was calculatedat each temperature in the sequence described in the chapter (2-3).

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. In the following description, “1 C” refers to acurrent value at which the discharge operation is expected to beterminated in one hour by discharging the battery from a full-chargestate of 4.2 V to a voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the ambient temperature to 25° C. and was then charged witha constant voltage of 4.2 V for one hour. Then, the battery wasdischarged with a constant current of 0.2 C to a voltage of 2.7 V. Then,a sealing portion of the battery was opened, and degassing was performedinside a glove box having a dew point controlled to −60° C. or lower.After the degassing, vacuum sealing was performed under the sameenvironment.

(2-2) 85° C. Full-Charge Storage Test for Multi-Layered Laminate-TypeBattery

For the battery subjected to the initial charging/discharging treatmentas described above in the chapter (2-1), the battery was charged with aconstant current of “1 C” to a voltage of 4.2 V by setting the batteryambient temperature to 25° C., and the battery was then charged with aconstant voltage of 4.2 V for a total of 3 hours. Then, this non-aqueoussecondary battery was stored in a thermostatic oven for 4 hours at 85°C. Then, the battery ambient temperature was recovered to 25° C.

(2-3) Ionic Conductivity Measurement

The electrolyte solution was put into a sealed cell (cell size: 24 mmdiameter by 0.35 mm thickness) produced by TOYO Corporation, was sealed,and was inserted into a holder (SH1-Z), and wiring was performed. Inaddition, the cell was put into the thermostatic oven, and themeasurement of electrochemical impedance spectroscopy was performed.Gold was used in the electrode. An argon glove box was used until theelectrolyte solution is collected, is filled to the sealed cell, and issealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature of the thermostatic oven was set to 20° C. and 0° C.,respectively, and the measurement was initiated after 1.5 hours from thetemperature setting. As the measurement data, data at the time pointthat a change of the data measured repeatedly at every 5 minutes islower than 0.1% was employed.

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

As the ionic conductivity, an initial ionic conductivity of theelectrolyte solution and an ionic conductivity of the electrolytesolution collected in the glove box having a dew point controlled to−60° C. or lower after the 85° C. storage test were obtained at 20° C.and 0° C., respectively.

Example 4

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:16:4” to obtain a mixed solvent. Inaddition, succinic anhydride (cyclic acid anhydride) was dissolved inthis mixed solvent finally up to 0.15 mass % as an electrolyte solution.In this case, the temperature of the mixed liquid was 30° C. Then, LiPF₆of 0.3 mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂CF)₂) of 1.3 mol,and LiPO₂F₂ of 5000 ppm were added per 1 L of the mixed solvent, so thatan electrolyte solution of Example 4 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved. Abattery was manufactured using this electrolyte solution on the basis ofthe method described above in the chapters (1-1) to (1-3), andevaluation was then performed in the sequence described in the chapters(2-1) and (2-2), so that, finally, the ionic conductivities at eachtemperature were calculated in the sequence described in the chapter(2-3).

Example 5

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:16:4” to obtain a mixed solvent. Inaddition, succinic anhydride (cyclic acid anhydride) was dissolved inthis mixed solvent finally up to 0.3 mass % as an electrolyte solution.In this case, the temperature of the mixed liquid was 30° C. Then, LiPF₆of 0.4 mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.7 mol,and LiPO₂F₂ of 5000 ppm were added per 1 L of the mixed solvent, so thatan electrolyte solution of Example 5 was obtained. In this case, theelectrolyte solution was produced by receiving only a thermal history of50° C. or lower. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapters (1-1) to (1-3), and evaluation was thenperformed in the sequence described in the chapters (2-1) and (2-2), sothat, finally, the ionic conductivities at each temperature werecalculated in the sequence described in the chapter (2-3).

Example 6

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “35:40:21:4” to obtain a mixed solvent. Inaddition, maleic anhydride (cyclic acid anhydride) was dissolved in thismixed solvent finally up to 0.15 mass % as an electrolyte solution. Inthis case, the temperature of the mixed liquid was 31° C. Then, LiPF₆ of1.0 mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.2 mol, andLiPO₂F₂ of 1000 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 6 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved. Abattery was manufactured using this electrolyte solution on the basis ofthe method described above in the chapters (1-1) to (1-3), andevaluation was then performed in the sequence described in the chapters(2-1) and (2-2), so that, finally, the ionic conductivities at eachtemperature were calculated in the sequence described in the chapter(2-3).

Example 7

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “65:6:22:7” to obtain a mixed solvent. In addition,phthalic anhydride (cyclic acid anhydride) was dissolved in this mixedsolvent finally up to 0.5 mass % as an electrolyte solution. In thiscase, the temperature of the mixed liquid was 29° C. Then, LiPF₆ of 0.6mol, lithium bis (trifluoromethane sulfonyl) imide (LiN(SO₂CF₃)₂) of 0.6mol, and LiPO₂F₂ of 500 ppm were added per 1 L of the mixed solvent, sothat an electrolyte solution of Example 7 was obtained. In this case,the electrolyte solution was produced by receiving only the thermalhistory of 50° C. or lower. For the obtained electrolyte solution, itwas visually inspected that all of the lithium salts are dissolved. Abattery was manufactured using this electrolyte solution on the basis ofthe method described above in the chapters (1-1) to (1-3), andevaluation was then performed in the sequence described in the chapters(2-1) and (2-2), so that, finally, the ionic conductivities at eachtemperature were calculated in the sequence described in the chapter(2-3).

Example 8

Acetonitrile (AcN), ethyl methyl carbonate (EMC), dimethyl carbonate(DMC), ethylene carbonate (EC), and vinylene carbonate (VC) were mixedunder an inert atmosphere at a volume ratio of “45:15:7:30:3” to obtaina mixed solvent. In addition, succinic anhydride (cyclic acid anhydride)was dissolved in this mixed solvent finally up to 0.2 mass % as anelectrolyte solution. In this case, the temperature of the mixed solventwas 31° C. Then, LiPF₆ of 0.6 mol, lithium bis (trifluoromethanesulfonyl) imide (LiN(SO₂CF₃)₂) of 0.2 mol, and LiPO₂F₂ of 100 ppm wereadded per 1 L of the mixed solvent, so that an electrolyte solution ofExample 8 was obtained. In this case, the temperature of the electrolytesolution was 42° C., and the electrolyte solution was produced byreceiving only a thermal history of 50° C. or lower. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapters(1-1) to (1-3), and evaluation was then performed in the sequencedescribed in the chapters (2-1) and (2-2), so that, finally, the ionicconductivities at each temperature were calculated in the sequencedescribed in the chapter (2-3).

Comparative Example 3

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:16:4” to obtain a mixed solvent. In thiscase, the temperature of the mixed solvent was 30° C. Then, LiPF₆ of 1.3mol per 1 L of this mixed solvent was put into a container, and themixed solvent was poured thereon. In addition, succinic anhydride(cyclic acid anhydride) of 0.05 mass % was dissolved, so that anelectrolyte solution of Comparative Example 3 was obtained. In thiscase, the temperature of the electrolyte solution was 63° C., and theelectrolyte solution was produced by receiving a thermal history of 50°C. or higher. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapters (1-1) to (1-3), and evaluation was thenperformed in the sequence described in the chapters (2-1) and (2-2), sothat, finally, the ionic conductivities at each temperature werecalculated in the sequence described in the chapter (2-3).

Comparative Example 4

Acetonitrile (AcN), diethyl carbonate (DEC), and vinylene carbonate (VC)were mixed under an inert atmosphere at a volume ratio of “47:42:11” toobtain a mixed solvent. In this case, the temperature of the mixedsolvent was 30° C. Then, LiPF₆ of 2.0 mol per 1 L of this mixed solventwas put into a container, and the mixed solvent was poured thereon, sothat an electrolyte solution of Comparative Example 4 was obtained. Inthis case, the temperature of the electrolyte solution was 68° C., andthe electrolyte solution was produced by receiving a thermal history of50° C. or higher. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapters (1-1) to (1-3), and evaluation was thenperformed in the sequence described in the chapters (2-1) and (2-2), sothat, finally, the ionic conductivities at each temperature werecalculated in the sequence described in the chapter (2-3).

Comparative Example 5

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “43:34:18:5” to obtain a mixed solvent. In this case,the temperature of the mixed solvent was 30° C. Then, LiPF₆ of 0.2 moland lithium bis (trifluoromethane sulfonyl) imide (LiN(SO₂CF₃)₂) of 1.0mol per 1 L of this mixed solvent was put into a container, and themixed solvent was poured thereon, so that an electrolyte solution ofComparative Example 5 was obtained. In this case, the temperature of theelectrolyte solution was 68° C., and the electrolyte solution wasproduced by receiving a thermal history of 50° C. or higher. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved. Note that cyclic acid anhydride is notadded in Comparative Example 2. A battery was manufactured using thiselectrolyte solution on the basis of the method described above in thechapters (1-1) to (1-3), and evaluation was then performed in thesequence described in the chapters (2-1) and (2-2), so that, finally,the ionic conductivities at each temperature were calculated in thesequence described in the chapter (2-3).

The following Table 3 shows compositions of each non-aqueous electrolytesolution in Examples 4 to 8 and Comparative Examples 3 to 5.

TABLE 3 Lithium salt Solvent Imide salt Additive AcN DEC EMC DMC ECLiPF₆ Content Cyclic acid (vol (vol (vol (vol (vol VC (mol/1 L (mol/1 Lanhydride LiPO₂F₂ Thermal %) %) %) %) %) (vol %) solvent) Type solvent)(mass %) (ppm) history Example 4 45 0 35 0 16 4 0.3 LiN(SO₂F)₂ 1.3 SAH0.15 5000 ≤50° C. Example 5 45 0 35 0 16 4 0.4 LiN(SO₂F)₂ 0.7 SAH 0.35000 ≤50° C. Example 6 35 0 40 0 21 4 1.0 LiN(SO₂F)₂ 0.2 MAH 0.15 1000≤50° C. Example 7 65 0 0 6 22 7 0.6 LiN(SO₂CF₃)₂ 0.6 PAH 0.5 500 ≤50° C.Example 8 45 0 15 7 30 3 0.6 LiN(SO₂CF₃)₂ 0.2 SAH 0.2 100 ≤50° C.Comparative 45 0 35 0 16 4 1.3 — — SAH 0.05 —  >60° C. Example 3Comparative 47 42 0 0 0 11 2.0 — — — —  >60° C. Example 4 Comparative 4334 0 0 18 5 0.2 LiN(SO₂CF₃)₂ 1 — —  >60° C. Example 5

The following Table 4 shows the ionic conductivities in Examples 4 to 8and Comparative Examples 3 to 5.

TABLE 4 Ion conductivity Initial ion after 85° C. conductivity storagetest [mS/cm] [mS/cm] 20° C. 0° C. 20° C. 0° C. Example 4 21.4 16.0 20.114.7 Example 5 19.5 15.5 18.2 14.4 Example 6 19.0 15.5 17.9 14.0 Example7 20.1 15.0 19.0 13.8 Example 8 19.7 15.3 18.0 14.2 Comparative Example3 19.5 14.5 18.2 9.8 Comparative Example 4 17.8 14.8 16.3 9.4Comparative Example 5 17.9 12.6 16.1 8.9

As shown in Table 4 described above, it was recognized that the initialionic conductivity does not significantly change even when thetemperature changes from 20° C. to 0° C. in Examples 4 to 8 andComparative Examples 3 and 4, the 0° C. ionic conductivity isapproximately 15 mS/cm or higher in Examples 4 to 8, and the 0° C. ionicconductivity is approximately 10 mS/cm or higher in Comparative Examples3 to 5.

Meanwhile, for the ionic conductivity after the storage test for 4 hoursat 85° C., there was a significant difference between Examples 4 to 8and Comparative Examples 3 to 5. That is, in the examples, the 0° C.ionic conductivity after the storage test for 4 hours at 85° C. was 10mS/cm or higher. Meanwhile, in the comparative examples, the 0° C. ionicconductivity after the storage test for 4 hours at 85° C. was lower than10 mS/cm. In the examples, the 0° C. ionic conductivity after thestorage test for 4 hours at 85° C. may be set to preferably 12 mS/cm orhigher.

As shown in Table 3, the non-aqueous electrolyte solutions of Examples 4to 8 contain acetonitrile, lithium salts, cyclic acid anhydride, andLiPF₆ and are produced with a thermal history of 50° C. or lower.

On the basis of the experimental results of the examples and thecomparative examples, it was preferable that the electrolyte solution ispreferably obtained by adding acetonitrile and cyclic acid anhydride andthen adding LiPF₆. As a result, an abrupt temperature increase at thetime of adding LiPF₆ is suppressed, and the cyclic acid anhydride reactssacrificially, so that it is possible to suppress generation of HF thatmay cause an increase of the internal resistance.

On the basis of the examples, it was preferable that a temperatureincrease at the time of adding the LiPF₆ is suppressed to 50° C. orlower. As a result, it is possible to suppress thermal decomposition ofLiPF₆ generated at 60° C. or higher.

Examples of the tenth to fourteenth embodiments will now be described.

<Evaluation on Low-Temperature Characteristics of Non-aqueousElectrolyte Solution>

(1-1) Measurement of Electrochemical Impedance Spectroscopy

The prepared electrolyte solution was put into a sealed cell (cell size:24 mm diameter by 0.35 mm thickness) produced by TOYO Corporation, wassealed, and was inserted into a holder (SH1-Z), and wiring wasperformed. The cell was put into the thermostatic oven, and measurementof electrochemical impedance spectroscopy was performed. Gold was usedin the electrode. An argon glove box having a dew point controlled to−60° C. or lower was used until the electrolyte solution is collected,is filled to the sealed cell, and is sealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature was set to four levels, that is, −30° C., −10° C., 0° C.,and 20° C., and the measurement was initiated after 1.5 hours from eachtemperature setting. As the measurement data, data at the time pointthat a change of the data measured repeatedly at every 5 minutes islower than 0.1% was employed.

(1-2) Ionic Conductivity

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

Example 9

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “50:28.5:20:1.5”. In addition, succinic anhydride (SAH)of 0.4 mass % was dissolved. Furthermore, LiPF₆ of 0.4 mol and lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.9 mol were added per 1 L ofthis mixed liquid, and LiPO₂F₂ of 50 ppm was dissolved, so as to obtainan electrolyte solution of Example 9. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. For this electrolyte solution, the ionic conductivities ateach temperature were calculated in the sequence described in thechapters (1-1) and (1-2).

Example 10

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “60:21:15:2”. In addition, succinic anhydride (SAH) of0.14 mass % was dissolved. Furthermore, LiPF₆ of 0.6 mol and lithium bis(trifluoromethane sulfonyl) imide (LiN(SO₂CF₃)₂) of 0.6 mol were addedper 1 L of this mixed liquid, and LiPO₂F₂ of 500 ppm and1-methyl-1H-benzotriazole (MBTA) of 0.5 mass % were dissolved, so as toobtain an electrolyte solution of Example 10. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. For this electrolyte solution, the ionicconductivities at each temperature were calculated in the sequencedescribed in the chapters (1-1) and (1-2).

Example 11

Acetonitrile (AcN), dimethyl carbonate (DMC), ethyl methyl carbonate(EMC), ethylene carbonate (EC), and vinylene carbonate (VC) were mixedunder an inert atmosphere at a volume ratio of “40:10:20:28:2”. Inaddition, succinic anhydride (SAH) of 0.2 mass % was dissolved.Furthermore, LiPF₆ of 0.3 mol and lithium bis (fluorosulfonyl) imide(LiN(SO₂F)₂) of 1.0 mol were added per 1 L of this mixed liquid, andLiPO₂F₂ of 2000 ppm and 1-methyl-1H-benzotriazole (MBTA) of 0.15 mass %were dissolved, so as to obtain an electrolyte solution of Example 11.For the obtained electrolyte solution, it was visually inspected thatall of the lithium salts are dissolved. For this electrolyte solution,the ionic conductivities at each temperature were calculated in thesequence described in the chapters (1-1) and (1-2).

Comparative Example 6

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “8:53:31:8”. In addition, succinic anhydride (SAH) of0.4 mass % was dissolved. Furthermore, LiPF₆ of 1.4 mol was added per 1L of this mixed liquid, and 1-methyl-1H-benzotriazole (MBTA) of 0.01mass % was dissolved, so as to obtain an electrolyte solution ofComparative Example 6. In Comparative Example 6, LiPO₂F₂ is not added.For the obtained electrolyte solution, it was visually inspected thatall of the lithium salts are dissolved. For this electrolyte solution,the ionic conductivities at each temperature were calculated in thesequence described in the chapters (1-1) and (1-2).

The following Table 5 shows compositions of each non-aqueous electrolytesolution in Examples 9 to 11 and Comparative Example 6.

TABLE 5 Lithium salt Additive Linear Solvent Imide salt Nitrogen-carbonate/ AcN DEC DMC EMC EC VC LiPF₆ Content Cyclic acid containingAcN (vol (vol (vol (vol (vol (vol (mol/1 L (mol/1 L anhydride LiPO₂F₂compound (molar %) %) %) %) %) %) solvent) Type solvent) (mass %) (ppm)(mass %) ratio) Example 9 50 28.5 0 0 20 1.5 0.4 LiN(SO₂F)₂ 0.9 SAH 0.450 — 0.25 Example 10 60 21 0 0 17 2 0.6 LiN(SO₂CF₃)₂ 0.6 SAH 0.14 500MBTA 0.5 0.15 Example 11 40 0 10 20 28 2 0.3 LiN(SO₂F)₂ 1.0 SAH 0.2 2000MBTA 0.15 0.44 Comparative 8 53 0 0 31 8 1.4 — — SAH 0.4 — MBTA 0.012.87 Example 6

The following Table 6 shows the ionic conductivities in Examples 9 to 11and Comparative Example 6.

TABLE 6 Ion conductivity [mS/cm] 20° C. 0° C. −10° C. −30° C. Example 921.9 15.5 12.5 7.1 Example 10 11.8 8.7 7.2 3.1 Example 11 20.6 14.8 11.96.5 Comparative Example 6 12.6 7.8 4.3 1.3

As shown in Table 6 described above, it was recognized that the −10° C.ionic conductivity is 7 mS/cm or higher in Examples 9 to 11. Inaddition, it was recognized that the −30° C. ionic conductivity is 3mS/cm or higher in Examples 9 to 11. Meanwhile, it was recognized that,in Comparative Example 6, the −10° C. ionic conductivity is 5 mS/cm orlower, and the −30° C. ionic conductivity is 2 mS/cm or lower.

On the basis of this experiment, it was preferable that the non-aqueouselectrolyte solution preferably contains LiPF₆ as lithium salt, lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) or lithium bis (trifluoromethanesulfonyl) imide (LiN(SO₂CF₃)₂) as imide salt, acetonitrile as a solvent,and cyclic acid anhydride and LiPO₂F₂ as an additive. In addition, itwas preferable that a ratio of acetonitrile relative to linear carbonateis 0.15% or higher and 2% or lower. As a result, it is possible tomaintain a high ionic conductivity even at a low temperature.

On the basis of the experimental results of the examples and thecomparative examples, it was preferable that the non-aqueous electrolytesolution contains the additives of a total mass of less than 5%. Here,the “additive” includes those generally used as a protection filmformation agent such as VC, MAH, SAH, PAH, and ES. As a result, theinterface (film) resistance is suppressed to be low, so that it ispossible to suppress cycle degradation at a low temperature.

On the basis of the experimental results of Examples 9 to 11, it waspreferable that the non-aqueous electrolyte solution contains LiPO₂F₂ of0.005 to 1 mass %, and the amount of vinylene carbonate is 4% or less.By setting the amount of LiPO₂F₂ and the amount of vinylene carbonate toa predetermined range, it is possible to provide a secondary batteryhaving excellent high-temperature durability and excellentlow-temperature performance.

Examples of the fifteenth to twentieth embodiments will now bedescribed.

<Manufacturing of Non-aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture.

N-methyl-2-pyrrolidone as a solvent was added to the obtained positiveelectrode mixture until a solid content of 68 mass %, and they werefurther mixed to prepare positive electrode mixture-containing slurry.

This positive electrode mixture-containing slurry was coated on onesurface of an aluminum foil having a thickness of 20 μm and a width of200 mm, which will serve as a positive electrode current collector,using a doctor blade method while adjusting the basis weight to 24.0mg/cm², and the solvent was dried and removed. Then, roll pressing wasperformed using a roll press machine to an actual electrode density of2.90 g/cm³, and a positive electrode having the positive-electrodeactive material layer and the positive electrode current collector wasobtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture.

Water as a solvent was added to the obtained negative electrode mixtureuntil a solid content of 45 mass %, and they were further mixed toprepare negative electrode mixture-containing slurry.

This negative electrode mixture-containing slurry was coated on onesurface of a copper foil having a thickness of 10 μm and a width of 200mm, which will serve as a negative electrode current collector, using adoctor blade method while adjusting the basis weight to 10.6 mg/cm², andthe solvent was dried and removed. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 1.50 g/cm³,and a negative electrode having the negative-electrode active materiallayer and the negative electrode current collector was obtained.

(1-3) Fabrication of Coin Type Non-Aqueous Secondary Battery

A polypropylene gasket was set on a CR2032 type battery casing(SUS304/Al-cladding), and the positive electrode obtained as describedabove was punched in a disk shape having a diameter of 16 mm and was seton a center of the gasket while the positive-electrode active materiallayer faces upward. In addition, glass fiber filter paper (glass fiberfiltering sheet, GA-100 produced by Advantech Co., Ltd.) punched in adisk shape having a diameter of 16 mm was set thereon, and anelectrolyte solution was injected by 150 μL. Then, the negativeelectrode obtained as described above and punched in a disk shape havinga diameter of 16 mm was set thereon while the negative-electrode activematerial layer faces downward. In addition, a spacer and a spring wereset, and a battery cap was fitted and crimped with a caulking machine.The overflowing electrolyte solution was wiped out with a waste cloth.The assembly was maintained at a temperature of 25° C. for 24 hours tofully adapt the electrolyte solution to the stacking component, so thata coin type non-aqueous secondary battery was obtained.

<Evaluation on High-Temperature Characteristic of Coin Type Non-AqueousSecondary Battery>

For the battery for evaluation obtained as described above, first,initial charging treatment was performed in the sequence of thefollowing chapter (2-1). Then, each battery was evaluated in thesequence of the chapter (2-2). Note that the charging/discharging wasperformed using a charging/discharging device ACD-01 (model name)produced by Asuka Electronics Co., Ltd. and a thermostatic oven PLM-63S(model name) produced by Futaba Kagaku Co., Ltd

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current

(2-1) Initial Charging/Discharging Treatment for Coin Type Non-aqueousSecondary Battery

The battery was charged with a constant current of 0.6 mA correspondingto “0.1 C” to a voltage of 4.2 V by setting the battery ambienttemperature to 25° C., and was then charged with a constant voltage of4.2 V for a total of 15 hours. Then, the battery was discharged to avoltage of 3.0 V with a constant current of 1.8 mA corresponding to “0.3C”. Initial efficiency was calculated by dividing the discharge capacityat this time by the charge capacity.

(2-2) 60° C. Full-Charge Storage Test of Coin Type Non-Aqueous SecondaryBattery

For the battery subjected to the initial charging/discharging treatmentas described above in the chapter (2-1), the battery was charged with aconstant current of 6 mA corresponding to “1 C” to a voltage of 4.2 V bysetting the battery ambient temperature to 25° C., and was then chargedwith a constant voltage of 4.2 V for a total of 3 hours. Then, thisnon-aqueous secondary battery was stored in a thermostatic oven having atemperature of 60° C. for 720 hours. Then, the battery ambienttemperature was recovered to 25° C.

(2-3) Measurement of Electrochemical Impedance Spectroscopy

The measurement of electrochemical impedance spectroscopy was performedusing a frequency response analyzer 1400 (model name) produced byAMETEK, Inc. and potentio-galvanostat 1470E (model name) produced byAMETEK, Inc. An A.C. impedance value at 1 kHz was obtained by measuringimpedance from a voltage/current response signal by applying an ACsignal while changing the frequency 1000 kHz to 0.01 Hz. An amplitude ofthe applied AC voltage was set to “±5 mV”. Furthermore, the batteryambient temperature at the time of measurement of electrochemicalimpedance spectroscopy was set to 25° C.

As a non-aqueous secondary battery to be measured, a coin typenon-aqueous secondary battery not subjected to the 60° C. full-chargestorage test and a coin type non-aqueous secondary battery subjected tothe 60° C. full-charge storage test were employed using the methoddescribed above in the chapter (2-2).

The following resistance increase rates were calculated from suchresults.Resistance increase rate=(resistance value after 60° C. full-chargestorage test/resistance value before 60° C. full-charge storagetest)×100[%]

<Evaluation on Low-temperature Characteristics of Non-aqueousElectrolyte Solution>

(3-1) Cell Assembly and Measurement of Electrochemical ImpedanceSpectroscopy

The electrolyte solution prepared as described above was put into asealed cell (cell size: 24 mm diameter by 0.35 mm thickness) produced byTOYO Corporation, was sealed, and was inserted into a holder (SH1-Z),and wiring was performed. In addition, the cell was put into thethermostatic oven, and the measurement of electrochemical impedancespectroscopy was performed. Gold was used in the electrode. An argonglove box was used until the electrolyte solution is collected, isfilled to the sealed cell, and is sealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature was set to four levels, that is, −30° C., −10° C., 0° C.,and 20° C., and the measurement was initiated after 1.5 hours from eachtemperature setting. As the measurement data, data at the time pointthat a change of the data measured repeatedly at every 5 minutes islower than 0.1% was employed.

(3-2) Ionic Conductivity

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

Example 12

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “50:35:10:5”. In addition, maleic anhydride (MAH) of 0.2mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.7 mol were added per 1 L ofthis mixed liquid, and LiPO₂F₂ of 0.8 mass % (8000 ppm) was dissolved,so as to obtain an electrolyte solution of Example 15. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapters(1-1) to (1-3), and evaluation for the coin type non-aqueous secondarybattery was then performed in the sequence described in the chapters(2-1) to (2-3), so that the ionic conductivities at each temperaturewere calculated in the sequence described in the chapters (3-1) and(3-2).

Example 13

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “65:6:22:7”. In addition, phthalic anhydride (PAH) of0.5 mass % was dissolved. Furthermore, LiPF₆ of 0.5 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.7 mol were added per 1 L ofthis mixed solvent, and LiPO₂F₂ of 0.1 mass % (1000 ppm) was dissolved,so that an electrolyte solution of Example 13 was obtained. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved. A battery was manufactured using thiselectrolyte solution on the basis of the method described above in thechapters (1-1) to (1-3), and evaluation for the coin type non-aqueoussecondary battery was then performed in the sequence described in thechapters (2-1) to (2-3), so that the ionic conductivities at eachtemperature were calculated in the sequence described in the chapters(3-1) and (3-2).

Example 14

Acetonitrile (AcN), dimethyl carbonate (DMC), ethyl methyl carbonate(EMC), ethylene carbonate (EC), and vinylene carbonate (VC) were mixedunder an inert atmosphere at a volume ratio of “40:10:19:29:2”. Inaddition, succinic anhydride (SAH) of 0.2 mass % was dissolved.Furthermore, LiPF₆ of 0.4 mol and lithium bis (fluorosulfonyl) imide(LiN(SO₂F)₂) of 0.8 mol were added per 1 L of this mixed solvent, andLiPO₂F₂ of 0.1 mass % (1000 ppm) was dissolved, so that an electrolytesolution of Example 14 was obtained. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. A battery was manufactured using this electrolyte solution onthe basis of the method described above in the chapters (1-1) to (1-3),and evaluation for the coin type non-aqueous secondary battery was thenperformed in the sequence described in the chapters (2-1) to (2-3), sothat the ionic conductivities at each temperature were calculated in thesequence described in the chapters (3-1) and (3-2).

Example 15

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:16:4”. In addition, succinic anhydride (SAH)of 0.15 mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.3 mol were added per 1 L ofthis mixed solvent, and LiPO₂F₂ of 0.1 mass % (1000 ppm) was dissolved,so that an electrolyte solution of Example 15 was obtained. A batterywas manufactured using this electrolyte solution on the basis of themethod described above in the chapters (1-1) to (1-3), and evaluationfor the coin type non-aqueous secondary battery was then performed inthe sequence described in the chapters (2-1) to (2-3), so that the ionicconductivities at each temperature were calculated in the sequencedescribed in the chapters (3-1) and (3-2).

Example 16

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “50:35:10:5”. In addition, maleic anhydride (MAH) of 0.2mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.0 mol were added per 1 L of themixed solvent, and LiPO₂F₂ of 0.5 mass % (5000 ppm) was dissolved, sothat an electrolyte solution of Example 16 was obtained. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapters (1-1) to (1-3), and evaluation for thecoin type non-aqueous secondary battery was then performed in thesequence described in the chapters (2-1) to (2-3), so that the ionicconductivities at each temperature were calculated in the sequencedescribed in the chapters (3-1) and (3-2).

Comparative Example 7

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “46:26:26:2”. In addition, LiPF₆ of 1.0 mol was addedper 1 L of the mixed solvent, so that an electrolyte solution ofComparative Example 7 was obtained. In Comparative Example 7, bothLiPO₂F₂ and cyclic acid anhydride are not added. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapters(1-1) to (1-3), and evaluation for the coin type non-aqueous secondarybattery was then performed in the sequence described in the chapters(2-1) to (2-3), so that the ionic conductivities at each temperaturewere calculated in the sequence described in the chapters (3-1) and(3-2).

Comparative Example 8

Acetonitrile (AcN), diethyl carbonate (DEC), and vinylene carbonate (VC)were mixed under an inert atmosphere at a volume ratio of “47:42:11”. Inaddition, maleic anhydride (MAH) of 0.05 mass % was dissolved.Furthermore, LiPF₆ of 1.3 mol and lithium bis (trifluoromethanesulfonyl) imide (LiN(SO₂CF₃)₂) of 1.0 mol were added per 1 L of themixed solvent, so that an electrolyte solution of Comparative Example 8was obtained. In Comparative Example 8, LiPO₂F₂ is not added. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved. A battery was manufactured using thiselectrolyte solution on the basis of the method described above in thechapters (1-1) to (1-3), and evaluation for the coin type non-aqueoussecondary battery was then performed in the sequence described in thechapters (2-1) to (2-3), so that the ionic conductivities at eachtemperature were calculated in the sequence described in the chapters(3-1) and (3-2).

Comparative Example 9

Lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 4.2 mol was dissolvedto the acetonitrile (AcN) of 1 L under an inert atmosphere to obtain anelectrolyte solution of Comparative Example 9. In Comparative Example 9,all of LiPF₆, LiPO₂F₂, and cyclic acid anhydride are not added. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved. A battery was manufactured using thiselectrolyte solution on the basis of the method described above in thechapters (1-1) to (1-3), and evaluation for the coin type non-aqueoussecondary battery was then performed in the sequence described in thechapters (2-1) to (2-3), so that the ionic conductivities at eachtemperature were calculated in the sequence described in the chapters(3-1) and (3-2).

The following Table 7 shows compositions of each non-aqueous electrolytesolutions in Examples 12 to 16 and Comparative Examples 7 to 9.

TABLE 7 Lithium salt Linear Solvent Imide salt Additive carbonate/ AcNDEC DMC EMC EC VC LiPF₆ Content Cyclic acid LiPF₆/AcN AcN (vol (vol (vol(vol (vol (vol (mol/1 L (mol/1 L anhydride LiPO₂F₂ (molar (molar %) %)%) %) %) %) solvent) Type solvent) (mass %) (ppm) ratio) ratio) Example12 50 35 0 0 10 5 0.3 LiN(SO₂F)₂ 1.7 MAH 0.2 8000 0.03 0.30 Example 1365 0 6 0 22 7 0.5 LiN(SO₂F)₂ 0.7 PAH 0.5 1000 0.04 0.06 Example 14 40 010 19 29 2 0.4 LiN(SO₂F)₂ 0.8 SAH 0.2 1000 0.05 0.40 Example 15 45 0 035 16 4 0.3 LiN(SO₂F)₂ 1.3 SAH 0.15 1000 0.03 0.40 Example 16 50 35 0 010 5 0.3 LiN(SO₂F)₂ 1.0 MAH 0.2 5000 0.03 0.30 Comparative 46 0 26 0 262 1.0 — — — — 0.11 0.35 Example 7 Comparative 47 42 0 0 0 11 1.3LiN(SO₂CF₃)₂ 1.0 MAH 0.05 — 0.15 0.39 Example 8 Comparative 100 0 0 0 00 0 LiN(SO₂F)₂ 4.2 — — 0.00 0.00 Example 9

The following Table 8 shows the resistance increase rates in thefull-charge storage test in Examples 12 to 16 and Comparative Examples 7to 9.

TABLE 8 A.C. impedance value at 1 kHz Resistance [Ω] increase Beforestorage After storage rate test test [%] Determination Example 12 3.16.3 203 ∘ Example 13 3.0 7.2 240 ∘ Example 14 2.7 6.1 226 ∘ Example 152.5 5.7 228 ∘ Example 16 3.1 6.3 203 ∘ Comparative 3.0 16.9 563 xExample 7 Comparative 3.0 15.2 507 x Example 8 Comparative 3.9 20.1 515x Example 9

The following Table 9 shows ionic conductivities in Examples 12 to 16and Comparative Examples 7 to 9.

TABLE 9 Ion conductivity [mS/cm] 20° C. 0° C. −10° C. 30° C. Example 1219.0 15.5 12.5 6.6 Example 13 20.0 15.5 12.0 6.2 Example 14 20.1 15.712.2 6.5 Example 15 21.0 16.0 13.5 7.1 Example 16 19.0 15.5 12.5 6.6Comparative Example 7 17.5 12.0 5.7 1.6 Comparative Example 8 20.5 158.2 2.9 Comparative Example 9 19.6 12.9 6.2 2.0

As shown in Table 8 described above, it was recognized that theresistance increase rates are lower than 400% in all of Examples 12 to16. In addition, it was recognized that the resistance increase ratesare lower than 300% and 250% in all of Examples 12 to 16.

As shown in Table 9 described above, it was recognized that the −10° C.ionic conductivity is 10 mS/cm or higher in Examples 12 to 16. Inaddition, it was recognized that the −10° C. ionic conductivity is 12mS/cm or higher in Examples 12 to 16. Furthermore, it was recognizedthat the −10° C. ionic conductivity is 12.5 mS/cm or higher in Examples12, 15, and 16.

As shown in Table 9 described above, it was recognized that the −30° C.ionic conductivity is 5 mS/cm or higher in Examples 12 to 16. Inaddition, it was recognized that the −30° C. ionic conductivity is 6mS/cm or higher in Examples 12 to 16. Furthermore, it was recognizedthat the −30° C. ionic conductivity is 6.5 mS/cm or higher in Examples12, and 14 to 16.

On the basis of the aforementioned description, it was recognized thatthe LiPF₆ acetonitrile electrolyte solution preferably contains LiPO₂F₂,cyclic acid anhydride, and imide salt. As a result, it is possible tosuppress a resistance increase during high-temperature heating andobtain an excellent low-temperature characteristic.

On the basis of the experimental results of the examples and thecomparative examples, it was recognized that LiPO₂F₂ of 0.005 to 1 mass% and cyclic acid anhydride of 0.01 to 1 mass % are preferably added tothe LiPF₆-based acetonitrile electrolyte solution, and the imide salt ispreferably added with a molarity relationship of “LiPF₆≤imide salt”. Asa result, it is possible to reinforce the positive electrode film due toLiPO₂F₂ and imide salt and suppress a resistance increase duringhigh-temperature heating. The imide salt itself exhibits excellentlow-temperature characteristics.

In Examples 13 to 16, LiPO₂F₂ of 0.005 to 1 mass % with respect to theacetonitrile electrolyte solution is added, and cyclic acid anhydride of0.01 to 1 mass % with respect to the electrolyte solution is added. Inaddition, the content of imide salt is 0.5 to 3 mol relative to thenon-aqueous solvent of “1 L”. As a result, it is possible to reinforcethe positive electrode film due to the LiPO₂F₂ and the imide salt andsuppress a resistance increase during high-temperature heating. Inaddition, it is possible to exhibit excellent low-temperaturecharacteristics due to the imide salt.

Examples of the twenty first to twenty third embodiments will now bedescribed.

<Heated NMR Measurement for Electrolyte Solution>

Inside an argon box, the electrolyte solutions of the examples and thecomparative examples were collected in an inner tube of an NMR tube(having a diameter of 3 mm), were capped, and were sealed with aparafilm. The inner tube of the NMR tube was taken out of the argon box,and was inserted into an outer tube containing a DMSO-d6 solution addedwith C₆H₂F₄, so that NMR measurement based on a dual tube method wasperformed. As the NMR measurement device, ECS400 produced by JEOLRESONANCE, Ltd. was employed. As the measurement condition, a pulsewidth was set to 45° C., the number of integrations was set to 256, astandby time for a temperature rise to 25° C. was set to 5 seconds, astandby time to 60° C. was set to 7 seconds, and a standby time to 85°C. was set to 10 seconds. The test result is shown in Table 11.

Example 17

An electrolyte solution was prepared by mixing a predetermined amount ofvarious solvents and additives as shown in the following Table 10. Thatis, acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate(EC), and vinylene carbonate (VC) were added and mixed at a volume ratioof “47:19:30:4”. In addition, maleic anhydride (MAH) of 0.2 mass % wasadded. Furthermore, LiPF₆ of 0.5 mol, lithium bis (trifluoromethanesulfonyl) imide (LiN(SO₂CF₃)₂) of 0.6 mol, and LiPO₂F₂ of 50 ppm wereadded per 1 L of the non-aqueous solvent of this mixed liquid, so as toobtain an electrolyte solution of Example 17. For this electrolytesolution, the heated NMR measurement described above was performed.

Example 18

An electrolyte solution was prepared by mixing a predetermined amount ofvarious solvents and additives as shown in the following Table 10. Thatis, acetonitrile (AcN), dimethyl carbonate (DMC), ethyl methyl carbonate(EMC), ethylene carbonate (EC), and vinylene carbonate (VC) were addedand mixed at a volume ratio of “35:19:15:28:3”. In addition, succinicanhydride (SAH) of 0.2 mass % was added. Furthermore, LiPF₆ of 0.5 mol,lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.8 mol, and LiPO₂F₂of 100 ppm were added per 1 L of the non-aqueous solvent of this mixedliquid, so as to obtain an electrolyte solution of Example 18. For thiselectrolyte solution, the heated NMR measurement described above wasperformed.

Comparative Example 10

An electrolyte solution was prepared by mixing a predetermined amount ofvarious solvents and additives as shown in the following Table 10. Thatis, acetonitrile (AcN), vinylene carbonate (VC), and propylene carbonate(PC) were added and mixed at a volume ratio of “60:10:30”. In addition,LiPF₆ of 1.0 mol was added per 1 L of the non-aqueous solvent of thismixed liquid, so as to obtain an electrolyte solution of ComparativeExample 10. For this electrolyte solution, the heated NMR measurementdescribed above was performed.

Comparative Example 11

An electrolyte solution was prepared by mixing a predetermined amount ofvarious solvents and additives as shown in the following Table 11. Thatis, acetonitrile (AcN), vinylene carbonate (VC), and propylene carbonate(PC) were added and mixed at a volume ratio of “46:4:50”. In addition,LiPF₆ of 1.0 mol was added per 1 L of the non-aqueous solvent of thismixed liquid, so as to obtain an electrolyte solution of ComparativeExample 11. For this electrolyte solution, the heated NMR measurementdescribed above was performed.

Comparative Example 12

An electrolyte solution was prepared by mixing a predetermined amount ofvarious solvents and additives as shown in the following Table 10. Thatis, acetonitrile (AcN), ethylene carbonate (EC), vinylene carbonate(VC), and propylene carbonate (PC) were added and mixed at a volumeratio of “38:30:2:30”. In addition, LiPF₆ of 1.0 mol was added per 1 Lof the non-aqueous solvent of this mixed liquid, so as to obtain anelectrolyte solution of Comparative Example 12. For this electrolytesolution, the heated NMR measurement described above was performed.

TABLE 10 Lithium salt Imide salt Additive Solvent LiPF₆ Content Cyclicacid AcN DEC DMC EMC EC VC PC (mol/1 L (mol/1 L anhydride LiPO₂F₂ (vol%) (vol %) (vol %) (vol %) (vol %) (vol %) (vol %) solvent) Typesolvent) (mass %) (ppm) Example 17 47 19 0 0 30 4 0 0.5 LiN(SO₂CF₃)₂ 0.6MAH 0.2 50 Example 18 35 0 19 15 28 3 0 0.5 LiN(SO₂F)₂ 0.8 SAH 0.2 100Comparative 60 0 0 0 0 10 30 1 — — — — Example 10 Comparative 46 0 0 0 04 50 1 — — — — Example 11 Comparative 38 0 0 0 30 2 30 1 — — — — Example12

In an experiment, the HF generation amount was measured at temperaturesof 25° C., 60° C., and 85° C. for Examples 17 and 18 and ComparativeExamples 10 to 12. The experimental results thereof are shown in Table11 described above.

TABLE 11 HF generation amount (ppm) 25° C. 60° C. 85° C. Example 17 2136 61 Example 18 22 35 60 Comparative Example 10 28 216 360 ComparativeExample 11 24 235 352 Comparative Example 12 25 182 298

As shown in Table 11, it was recognized that the HF generation amount issufficiently reduced in the examples, compared to the comparativeexamples.

From this experimental result, it was recognized that the LiPF₆-basedacetonitrile electrolytic solution containing LiPO₂F₂ and cyclic acidanhydride is preferably diluted with a carbonate solvent. As a result,it is possible to reinforce the negative electrode SEI due to theLiPO₂F₂ and the cyclic acid anhydride and reduce the HF generationamount at a temperature of 50 to 60° C.

On the basis of the experimental results of the examples and thecomparative examples, it was preferable that the LiPF₆-basedacetonitrile electrolyte solution is diluted with a non-aqueous solventthat does not have saturated tertiary carbon. Since a proton can beeasily released from carbonate having saturated secondary carbon (forexample, propylene carbonate), it tends to promote generation of HF at atemperature of 50 to 60° C. However, if it is diluted with a non-aqueoussolvent that does not have saturated tertiary carbon, it is possible tosuppress generation of HF.

A twenty third embodiment will now be described.

<Manufacturing of Non-Aqueous Secondary Battery>

<Fabrication of Positive Electrode>

A composite oxide (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂) of lithium, nickel,manganese, and cobalt as the positive-electrode active material,acetylene black powder as the conductive aid, and polyvinylidenefluoride (PVDF) as the binder were mixed at a mass ratio of “100:3.5:3”to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as asolvent was added to the obtained positive electrode mixture, and theywere further mixed to prepare positive electrode mixture-containingslurry. This positive electrode mixture-containing slurry was coated onone surface of an aluminum foil having a thickness of 15 μm, which willserve as a positive electrode current collector, while adjusting thebasis weight to approximately 95.0 g/m². When the positive electrodemixture-containing slurry was coated on the aluminum foil, an uncoatedregion was formed so as to expose a part of the aluminum foil. Then,roll pressing was performed using a roll press machine until thepositive-electrode active material layer has a density of 2.74 g/cm³, sothat a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 30 mm by 50 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, carboxymethylcellulose as the binder, and styrene-butadiene latex as the binder weremixed at a mass ratio of “100:1.1:1.5” to obtain a negative electrodemixture. An appropriate amount of water was added to the obtainednegative electrode mixture, and they were mixed sufficiently to preparenegative electrode mixture-containing slurry. This slurry was coated onone surface of a copper foil having a thickness of 10 μm to a constantthickness while adjusting the basis weight to approximately 61.0 g/m².When the negative electrode mixture-containing slurry was coated on thecopper foil, an uncoated region was formed so as to expose a part of thecopper foil. Then, roll pressing was performed using a roll pressmachine until the negative-electrode active material layer has a densityof 1.20 g/cm³, so that a negative electrode having thenegative-electrode active material layer and the negative electrodecurrent collector was obtained.

Then, this negative electrode was cut such that the negative electrodemixture layer has an area of 32 mm by 52 mm, and the exposed portion ofthe copper foil is included. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 hours at 80° C., so that alead-attached negative electrode was obtained.

<Assembly of Single-Layered Laminate-Type Battery>

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene microporousmembrane separator (having a thickness of 21 μm) while the mixture coatsurfaces of each electrode face each other, so that a laminatedelectrode structure was obtained. This laminated electrode structure washoused in an aluminum laminated sheet package having a size of 90 mm by80 mm, and vacuum drying was performed for 5 hours at 80° C. in order toremove moisture. Subsequently, each of the electrolyte solutionsdescribed below was injected into the package, and the package wassealed, so that a single-layered laminate type (pouch type) non-aqueoussecondary battery (hereinafter, simply also referred to as“single-layered laminate-type battery”) was manufactured. Thissingle-layered laminate-type battery has a design capacity value of 23mAh and a rated voltage value of 4.2 V.

<Evaluation of Single-Layered Laminate-Type Battery>

For the battery for evaluation obtained as described above, first,initial charging treatment was performed in the sequence of thefollowing chapter (1-1). Then, each battery was evaluated in thesequence of the chapter (1-2). Note that the charging/discharging wasperformed using a charging/discharging device ACD-01 (model name)produced by Asuka Electronics Co., Ltd. and a thermostatic oven PLM-63S(model name) produced by Futaba Kagaku Co., Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 2.5 V at a constant current.

(1-1) Initial Charging/Discharging Treatment of Single-LayeredLaminate-Type Battery

The battery was charged with a constant current of 2.3 mA correspondingto “0.1 C” to a voltage of 4.2 V by setting the battery ambienttemperature to 25° C. and was then charged with a constant voltage of4.2 V for a total of 1.5 hours. Then, the battery was discharged with aconstant current of 6.9 mA corresponding to “0.3 C” to a voltage of 2.5V. Initial efficiency was calculated by dividing the discharge capacityat this time by the charge capacity.

(1-2) −10° C. Charging/Discharging Cycle Test for Single-LayeredLaminate-Type Battery

A cycle test was performed for the battery subjected to the initialcharging/discharging treatment using the method described in theaforementioned chapter (1-1). Note that the cycle test was initiated 3hours later after the battery ambient temperature is set to −10° C.First, the battery was charged with a constant current of 4.6 mAcorresponding to “0.2 C” to a voltage of 4.2 V, and was then chargedwith a constant voltage of 4.2 V for a total of 3 hours. Then, thebattery was discharged with a constant current of 4.6 mA to a voltage of2.5 V. By setting one charge operation and one discharge operation as asingle cycle, the charging/discharging was performed for 20 cycles. Thedischarge capacity of the twentieth cycle was set as a capacityretention rate by assuming that the discharge capacity of the firstcycle is 100%.

<Evaluation on Low-Temperature Characteristic of Non-Aqueous ElectrolyteSolution>

(2-1) Measurement of Electrochemical Impedance Spectroscopy

The electrolyte solution prepared as described above was put into asealed cell (cell size: 24 mm diameter by 0.35 mm thickness) produced byTOYO Corporation, was sealed, and was inserted into a holder (SH1-Z),and wiring was performed. In addition, the cell was put into thethermostatic oven, and the measurement of electrochemical impedancespectroscopy was performed. Gold was used in the electrode. An argonglove box having a dew point controlled to −60° C. or lower was useduntil the electrolyte solution is collected, is filled to the sealedcell, and is sealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature was set to four levels, that is, −30° C., −10° C., 0° C.,and 20° C., and the measurement was initiated after 1.5 hours from eachtemperature setting. As the measurement data, data at the time pointthat a change of the data measured repeatedly at every 5 minutes islower than 0.1% was employed.

(2-2) Ionic Conductivity

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

Example 19

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “50:28:20:2”. In addition, succinic anhydride (SAH)of 0.2 mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.0 mol were added per 1 L ofthe mixed liquid, and LiPO₂F₂ of 0.1 mass % (1000 ppm) was added, so asto obtain an electrolyte solution of Example 19. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapter(1-1), and evaluation of the coin type non-aqueous secondary battery wasperformed in the sequence described above in the chapter (1-2).Furthermore, the ionic conductivity at each temperature was calculatedfor the produced electrolyte solution in the sequence described in thechapters (2-1) and (2-2).

Example 20

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “70:13:15:2”. In addition, succinic anhydride (SAH)of 0.2 mass % was dissolved. Furthermore, LiPF₆ of 0.4 mol and lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.9 mol were added per 1 L ofthe mixed liquid, and LiPO₂F₂ of 0.1 mass % (1000 ppm) was added, so asto obtain an electrolyte solution of Example 20. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapter(1-1), and evaluation of the coin type non-aqueous secondary battery wasperformed in the sequence described above in the chapter (1-2).Furthermore, the ionic conductivity at each temperature was calculatedfor the produced electrolyte solution in the sequence described in thechapters (2-1) and (2-2).

Example 21

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “50:28.5:20:1.5”. In addition, succinic anhydride (SAH)of 0.4 mass % was dissolved. Furthermore, LiPF₆ of 0.4 mol and lithiumbis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.9 mol were added per 1 L ofthe mixed liquid, and LiPO₂F₂ of 50 ppm was added, so as to obtain anelectrolyte solution of Example 21. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. A battery was manufactured using this electrolyte solution onthe basis of the method described above in the chapter (1-1), andevaluation of the coin type non-aqueous secondary battery was performedin the sequence described above in the chapter (1-2). Furthermore, theionic conductivity at each temperature was calculated for the producedelectrolyte solution in the sequence described in the chapters (2-1) and(2-2).

Example 22

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “49:28:21:2”. In addition, succinic anhydride (SAH) of0.2 mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.0 mol were added per 1 L of themixed liquid, and LiPO₂F₂ of 50 ppm and 1-methyl-1H-benzotriazole (MBTA)of 0.25 mass % were dissolved, so as to obtain an electrolyte solutionof Example 22. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapter (1-1), and evaluation of the coin typenon-aqueous secondary battery was performed in the sequence describedabove in the chapter (1-2). Furthermore, the ionic conductivity at eachtemperature was calculated for the produced electrolyte solution in thesequence described in the chapters (2-1) and (2-2).

Example 23

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “60:21:17:2”. In addition, succinic anhydride (SAH) of0.14 mass % was dissolved. Furthermore, LiPF₆ of 0.6 mol and lithium bis(trifluoromethane sulfonyl) imide (LiN(SO₂CF₃)₂) of 0.6 mol were addedper 1 L of the mixed liquid, and LiPO₂F₂ of 500 ppm and1-methyl-1H-benzotriazole (MBTA) of 0.5 mass % were dissolved, so as toobtain an electrolyte solution of Example 23. For the obtainedelectrolyte solution, it was visually inspected that all of the lithiumsalts are dissolved. A battery was manufactured using this electrolytesolution on the basis of the method described above in the chapter(1-1), and evaluation of the coin type non-aqueous secondary battery wasperformed in the sequence described above in the chapter (1-2).Furthermore, the ionic conductivity at each temperature was calculatedfor the produced electrolyte solution in the sequence described in thechapters (2-1) and (2-2).

Comparative Example 13

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “41:30:22:7”. In addition, succinic anhydride (SAH) of1.5 mass % was dissolved. Furthermore, LiPF₆ of 1.5 mol and lithium bis(trifluoromethane sulfonyl) imide (LiN(SO₂CF₃)₂) of 0.8 mol were addedper 1 L of the mixed liquid, so as to obtain an electrolyte solution ofComparative Example 13. In Comparative Example 13, the LiPO₂F₂ is notadded. For the obtained electrolyte solution, it was visually inspectedthat all of the lithium salts are dissolved. A battery was manufacturedusing this electrolyte solution on the basis of the method describedabove in the chapter (1-1), and evaluation of the coin type non-aqueoussecondary battery was performed in the sequence described above in thechapter (1-2). Furthermore, the ionic conductivity at each temperaturewas calculated for the produced electrolyte solution in the sequencedescribed in the chapters (2-1) and (2-2).

Comparative Example 14

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “8:53:31:8”. In addition, succinic anhydride (SAH) of0.4 mass % was dissolved. Furthermore, LiPF₆ of 1.4 mol was added per 1L of the mixed liquid, and 1-methyl-1H-benzotriazole (MBTA) of 0.01 mass% were dissolved, so as to obtain an electrolyte solution of ComparativeExample 14. In Comparative Example 14, the imide salt and the LiPO₂F₂are not added. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved. A battery wasmanufactured using this electrolyte solution on the basis of the methoddescribed above in the chapter (1-1), and evaluation of the coin typenon-aqueous secondary battery was performed in the sequence describedabove in the chapter (1-2). Furthermore, the ionic conductivity at eachtemperature was calculated for the produced electrolyte solution in thesequence described in the chapters (2-1) and (2-2).

Comparative Example 15

Acetonitrile (AcN), diethyl carbonate (DEC), dimethyl carbonate (DMC),ethylene carbonate (EC), and vinylene carbonate (VC) were mixed under aninert atmosphere at a volume ratio of “17:23:20:31:9”. In addition,succinic anhydride (SAH) of 0.4 mass % was dissolved. Furthermore, LiPF₆of 1.4 mol was added per 1 L of the mixed liquid, and LiPO₂F₂ of 50 ppmwere added, so as to obtain an electrolyte solution of ComparativeExample 15. In Comparative Example 15, the imide salt is not added. Forthe obtained electrolyte solution, it was visually inspected that all ofthe lithium salts are dissolved. A battery was manufactured using thiselectrolyte solution on the basis of the method described above in thechapter (1-1), and evaluation of the coin type non-aqueous secondarybattery was performed in the sequence described above in the chapter(1-2). Furthermore, the ionic conductivity at each temperature wascalculated for the produced electrolyte solution in the sequencedescribed in the chapters (2-1) and (2-2).

In the following description, compositions of each non-aqueouselectrolyte solution of Examples 19 to 23 and Comparative Examples 13 to15 will be described.

TABLE 12 Lithium salt Additive Linear Solvent Imide salt Nitrogen-carbonate/ AcN DEC DMC EMC EC VC LiPF₆ Content Cyclic acid containingAcN (vol (vol (vol (vol (vol (vol (mol/1 L (mol/1 L anhydride LiPO₂F₂compound (molar %) %) %) %) %) %) solvent) Type solvent) (mass %) (ppm)(mass %) ratio) Example 19 50 0 0 28 20 2 0.3 LiN(SO₂F)₂ 1.0 SAH 0.21000 0 0.29 Example 20 70 0 0 13 15 2 0.4 LiN(SO₂F)₂ 0.9 SAH 0.2 1000 —0.10 Example 21 50 28.5 0 0 20 1.5 0.4 LiN(SO₂F)₂ 0.9 SAH 0.4 50 — 0.25Example 22 49 28 0 0 21 2 0.3 LiN(SO₂F)₂ 1.0 SAH 0.2 50 MBTA 0.25 0.25Example 23 60 21 0 0 17 2 0.6 LiN(SO₂CF₃)₂ 0.6 SAH 0.14 500 MBTA 0.50.15 Comparative 41 30 0 0 22 7 1.5 LiN(SO₂CF₃)₂ 0.8 SAH 1.5 — — 0.32Example 13 Comparative 8 53 0 0 31 8 1.4 — — SAH 0.4 — MBTA 0.01 2.87Example 14 Comparative 17 23 20 0 31 9 1.4 — — SAH 0.4 50 — 1.32 Example15

The following Table 13 shows the ionic conductivities in Examples 19 to23 and Comparative Examples 13 to 15.

TABLE 13 Ion conductivity [mS/cm] 20° C. 0° C. −10° C. −30° C. Example19 22.0 15.6 13.2 7.5 Example 20 23.4 16.5 13.7 7.8 Example 21 21.9 15.512.5 7.1 Example 22 21.7 15.3 12.4 7.1 Example 23 11.8 8.7 7.2 3.1Comparative Example 13 16.9 10.5 5.8 1.8 Comparative Example 14 12.6 7.84.3 1.3 Comparative Example 15 15.7 9.7 5.2 1.6

TABLE 14 −10° C. cycle test Example 19 96% Example 20 97% Example 21 97%Example 22 95% Example 23 94% Comparative Example 13 35% ComparativeExample 14 20% Comparative Example 15 31%

As shown in Table 13, it was recognized that the −10° C. ionicconductivity is 7 mS/cm or higher in Examples 19 to 23. In addition, itwas recognized that the −10° C. ionic conductivity is 10 mS/cm or higherin Examples 19 to 22.

As shown above in Table 14, it was recognized the capacity retentionrate after the cycle test is 90% or higher in Examples 19 to 23.

In this experiment, it was preferable that the non-aqueous electrolytesolution contains LiPF₆ as the lithium salt, lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) or lithium bis (trifluoromethanesulfonyl) imide (LiN(SO₂CF₃)₂) as the imide salt, acetonitrile as thesolvent, and cyclic acid anhydride and LiPO₂F₂ as the additive. As aresult, since the interface (film) resistance is suppressed to be low,it is possible to suppress cycle degradation at a low temperature.

On the basis of the experimental results of the examples and thecomparative examples, it was preferable that the non-aqueous electrolytesolution contains the additives of a total mass of less than 5%. Here,the “additive” includes those generally used as a protection filmformation agent such as VC, MAH, SAH, PAH, and ES. As a result, theinterface (film) resistance is suppressed to be low, so that it ispossible to suppress cycle degradation at a low temperature.

On the basis of Examples 19 to 23, it was preferable that thenon-aqueous electrolyte solution contains LiPO₂F₂ of 0.005 to 1 mass %and vinylene carbonate of 4% or less. By setting the amount of LiPO₂F₂and the amount of vinylene carbonate to a predetermined range, it ispossible to provide a secondary battery having excellenthigh-temperature durability and excellent low-temperature performance.

Examples of the twenty fourth to twenty sixth embodiments will now bedescribed.

<Evaluation on Low-Temperature Characteristic of Non-Aqueous ElectrolyteSolution>

(1-1) Measurement of Electrochemical Impedance Spectroscopy

The prepared electrolyte solution was put into a sealed cell (cell size:24 mm diameter by 0.35 mm thickness) produced by TOYO Corporation, wassealed, and was inserted into a holder (SH1-Z), and wiring wasperformed. In addition, the cell was put into the thermostatic oven, andthe measurement of electrochemical impedance spectroscopy was performed.Gold was used in the electrode. An argon glove box was used until theelectrolyte solution is collected, is filled to the sealed cell, and issealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature was set to four levels, that is, −30° C., −10° C., 0° C.,and 20° C., and the measurement was initiated after 1.5 hours from eachtemperature setting. As the measurement data, data at the time pointthat a change of the data measured repeatedly at every 5 minutes islower than 0.1% was employed.

(2-2) Ionic Conductivity

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

Example 24

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “50:30:18:2”. In addition, phthalic anhydride (PAH) of0.2 mass % was dissolved. Furthermore, LiPF₆ of 0.3 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.0 mol were added per 1 L of themixed liquid, and LiPO₂F₂ of 500 ppm was dissolved, so as to obtain anelectrolyte solution of Example 24. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. For this electrolyte solution, the ionic conductivities ateach temperature were calculated in the sequence described in thechapters (1-1) and (1-2).

Example 25

Acetonitrile (AcN), diethyl carbonate (DEC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “60:32:5:3”. In addition, maleic anhydride (MAH) of 0.1mass % was dissolved. Furthermore, LiPF₆ of 0.5 mol and lithium bis(fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.6 mol were added per 1 L of themixed liquid, and LiPO₂F₂ of 1000 ppm was dissolved, so as to obtain anelectrolyte solution of Example 25. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. For this electrolyte solution, the ionic conductivities ateach temperature were calculated in the sequence described in thechapters (1-1) and (1-2).

Comparative Example 16

Ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were mixedunder an inert atmosphere at a volume ratio of “70:30”. In addition,LiPF₆ of 1.0 mol was added per 1 L of the mixed liquid, so as to obtainan electrolyte solution of Comparative Example 16. In ComparativeExample 16, the LiPO₂F₂ is not added. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved. For this electrolyte solution, the ionic conductivities ateach temperature were calculated in the sequence described in thechapters (1-1) and (1-2).

Comparative Example 17

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “10:30:50:10”, so as to obtain an electrolyte solutionof Comparative Example 17. In Comparative Example 17, the LiPO₂F₂ is notadded. For the obtained electrolyte solution, it was visually inspectedthat all of the lithium salts are dissolved. For this electrolytesolution, the ionic conductivities at each temperature were calculatedin the sequence described in the chapters (1-1) and (1-2).

The following description shows compositions of each non-aqueouselectrolyte solution in Examples 24 and 25 and Comparative Examples 16and 17.

TABLE 15 Lithium salt Solvent Imide salt Additive Linear AcN DEC DMC EMCEC VC LiPF₆ Content Cyclic acid LiPF₆/AcN carbonate/ (vol (vol (vol (vol(vol (vol (mol/1 L (mol/1 L anhydride LiPO₂F₂ (molar AcN %) %) %) %) %)%) solvent) Type solvent) (mass %) (ppm) ratio) (molar ratio) Example 2450 30 0 0 18 2 0.3 LiN(SO₂F)₂ 1.0 PAH 0.2 500 0.14 0.25 Example 25 60 320 0 5 3 0.5 LiN(SO₂F)₂ 0.6 MAH 0.1 1000 0.04 0.24 Comparative 0 0 0 7030 0 1.0 — — — 0 0.00 0.00 Example 16 Comparative 10 0 30 0 50 10 1.3 —— — 0 0.68 1.75 Example 17

The following Table 16 shows ionic conductivities in Examples 24 and 25and Comparative Examples 16 and 17.

TABLE 16 Ion conductivity [mS/cm] 20° C. 0° C. −10° C. −30° C. Example24 21.6 15.3 12.3 7.0 Example 25 17.6 13.4 9.1 5.3 Comparative Example16 8.7 5.5 4.0 1.8 Comparative Example 17 9.1 4.9 2.4 0.9

As shown in Table 16 described above, it was recognized that the 0° C.ionic conductivity is 10 mS/cm or higher, and preferably 13 mS/cm orhigher in Examples 24 and 25. In addition, as shown in Table 16described above, it was recognized that the −10° C. ionic conductivityis 9 mS/cm or higher in Examples 24 and 25. Furthermore, it wasrecognized that the −30° C. ionic conductivity is 5 mS/cm or higher inExamples 24 and 25.

In this experiment, it was recognized that the non-aqueous electrolytesolution containing LiPF₆ or LiPO₂F₂ as the lithium salt, acetonitrileas the solvent, and cyclic acid anhydride as the additive has a 0° C.ionic conductivity of 10 mS/cm or higher. As a result, the 0° C. ionicconductivity is higher than the 20° C. ionic conductivity of theexisting electrolyte solution (8.7 to 9.1 mS/cm).

On the basis of the experimental results of the examples and thecomparative examples, it is preferable that a particular ratio“LiPF₆/AcN” (affecting the amount of the aggregate) and a particularratio “linear carbonate/AcN” (affecting the solubility) are satisfied atthe same time.

Specifically, from Examples 24 and 25, it is preferable that theelectrolyte solution contains LiPF₆ and non-aqueous solvent, the contentof LiPF₆ is 1.5 mol or less with respect to the non-aqueous solvent of“1 L”, the non-aqueous solvent contains acetonitrile and linearcarbonate, the molar mixing ratio of LiPF₆ relative to acetonitrile is0.08 or higher and 0.4 or less, and the molar mixing ratio of linearcarbonate relative to acetonitrile is 0.3 or higher and 2 or lower. As aresult, it is possible to address a tradeoff problem between preventionof association of LiPF₆ (by increasing linear carbonate) and suppressionof reduction of the ionic conductivity at a low-temperature range (byincreasing acetonitrile).

Examples of the twenty seventh and twenty eighth embodiments will now bedescribed.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 17. Note that, in Table 17, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “EC” denotes ethylene carbonate, “VC” denotes vinylenecarbonate, “LiPF₆” denotes lithium hexafluorophosphate, “LiN(SO₂F)₂”denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denoteslithium bis (trifluoromethane sulfonyl) imide, “SAH” denotes succinicanhydride, “MAH” denotes maleic anhydride, “PAH” denotes phthalicanhydride, and “LiPO₂F₂” denotes lithium difluorophosphate.

Preparation was performed such that each component other than thelithium salt is a non-aqueous solvent, and a total amount of eachnon-aqueous solvent becomes “1 L”. The content of lithium salt is amolar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 17 Lithium salt Imide salt Additive Solvent Content Cyclic acidAcN DEC EMC EC VC LiPF₆ (mol/1 L anhydride LiPO₂F₂ (vol %) (vol %) (vol%) (vol %) (vol %) (mol/1 L solvent) Type solvent) (mass %) (mass %)Example 26 47 28 0 21 4 0.3 LiN(SO₂F)₂ 1.0 PAH 0.3 0.1 Example 27 38 060 0 2 0.3 LiN(SO₂F)₂ 2.0 SAH 0.5 0.5 Example 28 65 0 16 8 11 0.2LiN(SO₂CF₃)₂ 0.8 MAH 0.1 0.05 Comparative 0 0 33 67 0 1 — — — — Example18 Comparative 47 28 0 21 4 1.3 — — — — Example 19

<Measurement of Electrochemical Impedance Spectroscopy>

The prepared electrolyte solution was put into a sealed cell (cell size:24 mm diameter by 0.35 mm thickness) produced by TOYO Corporation, wassealed, and was inserted into a holder (SH1-Z), and wiring wasperformed. In addition, the cell was put into the thermostatic oven, andmeasurement of electrochemical impedance spectroscopy was performed.Gold was used in the electrode. An argon glove box was used until theelectrolyte solution is collected, is filled to the sealed cell, and issealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature of the thermostatic oven was set to five levels, that is,−20° C., −10° C., 0° C., 10° C. and 20° C., and the measurement wasinitiated after 1.5 hours from each temperature setting. As themeasurement data, data at the time point that a change of the datameasured repeatedly at every 5 minutes is lower than 0.1% was employed.

<Ionic Conductivity>

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

<Arrhenius Plot of Ionic Conductivity>

Using the Li ionic conductivities at each temperature obtained from theaforementioned formulas, the inclinations of the Arrhenius plot at −20to 0° C. and at 0 to 20° C. were obtained on the basis of the Arrheniusequation: σ=A exp(−Ea/kT), (“σ” denotes an ionic conductivity, “A”denotes a frequency factor, “k” denotes the Boltzmann constant, and “T”denotes the absolute temperature).

An electrolyte solution having the composition of Table 17 was preparedat a temperature of 25° C., and the cell was assembled using theaforementioned method, so that the measurement of electrochemicalimpedance spectroscopy was performed. A Nyquist diagram was created fromthe obtained data, and the Z′ value was read. From the aforementionedformulas, the ionic conductivity was calculated for Examples 26 to 28and Comparative Example 18. The inclinations of the Arrhenius plot at−20 to 0° C. and at 0 to 20° C. were obtained using the calculated ionicconductivity, and activation energy (Ea) was obtained from theinclinations of the Arrhenius plot. The result is shown in the followingTable 18.

TABLE 18 Activation energy (kJ/mol) Ea₁ Ea₂ (−20-0° C.) (0-20° C.)Ea₂/Ea₁ Example 26 13.5 11.5 0.852 Example 27 11.8 10.0 0.847 Example 2812.9 11.0 0.853 Comparative Example 18 19.9 15.9 0.799 ComparativeExample 19 16.0 16.0 0.516

As shown in Table 18, in all the comparative examples, it was recognizedthat the activation energies Ea₁ and Ea₂ at −20 to 0° C. and 0 to 20° C.are much higher than 15 kJ/mol. In comparison, in all the examples, itwas recognized that the activation energy Ea₁ at −20 to 0° C. is equalto or lower than 15 kJ/mol. In addition, in the examples, it wasrecognized that the activation energy Ea₂ at 0 to 20° C. is equal to orlower than 15 kJ/mol. Furthermore, the value obtained by dividing theactivation energy Ea₂ at 0 to 20° C. by the activation energy Ea₁ at −20to 0° C. (Ea₂/Ea₁) was much smaller than “1” in the comparativeexamples, compared to the examples. That is, in the comparativeexamples, the Ea₁ and Ea₂ are remarkably different. As a result, theelectrolyte solution is not stabilized energetically, and the ionicconductivity suffers from a discontinuous change in the comparativeexamples, compared to the examples. In comparison, in the examples, itwas recognized that the Ea₂/Ea₁ is stabilized energetically in thevicinity of “1”, and the ionic conductivity is stabilized even in alow-temperature range equal to or lower than 0° C.

In Examples 26 and 27, the electrolyte solution contains acetonitrileand LiPO₂F₂ and LiN(SO₂F)₂ (imide salt) as the lithium salt. Inaddition, in Example 28, the electrolyte solution contains acetonitrileand LiPO₂F₂ and LiN(SO₂CF₃)₂ (imide salt) as the lithium salt.

In Examples 26 to 28, the content of LiPO₂F₂ is 0.01 mass % or more and1 mass % or less with respect to the electrolyte solution. In addition,in the electrolyte solutions of Examples 26 to 28, it was recognizedthat a percentage of the molar quantity of imide salt relative to atotal molar quantity of the lithium salts contained in the electrolytesolution is 50% or higher. That is, it was recognized that the maincomponent of the lithium salt of the electrolyte solutions of Examples26 to 28 is imide salt.

Since the electrolyte solution of Comparative Example 19 containsacetonitrile, the electrode of the sealed cell using the electrolytesolution was stained. In comparison, in the electrolyte solutions ofExamples 26 to 28, although they contain acetonitrile, the electrode ofthe sealed cell using the electrolyte solution was not stained. This isbecause LiPO₂F₂ is contained.

Examples of the twenty ninth and thirtieth embodiments will now bedescribed.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 19. Note that, in Table 19, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EC” denotes ethylenecarbonate, “VC” denotes vinylene carbonate, “LiPF₆” denotes lithiumhexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis (fluorosulfonyl)imide, “LiN(SO₂CF₃)₂” denotes lithium bis (trifluoromethane sulfonyl)imide, “SAH” denotes succinic anhydride, “LiPO₂F₂” denotes lithiumdifluorophosphate, and “MBTA” denotes 1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 19 Additive Solvent Lithium salt Nitrogen- AcN LiPF₆ Imide saltCyclic acid containing (vol DEC EC VC (mol/1 L Content anhydride LiPO₂F₂compound %) (vol %) (vol %) (vol %) solvent) Type (mol/1 L solvent)(mass %) (mass %) (mass %) Example 29 45 30 21 4 0.3 LiN(SO₂F)₂ 1.0 SAH0.15 0.1 MBTA 0.3 Example 30 45 30 21 4 0.4 LiN(SO₂CF₃)₂ 0.6 SAH 0.150.1 MBTA 0.3 Comparative 45 30 21 4 0.3 LiN(SO₂CF₃)₂ 1.0 SAH 0.15 — —Example 20 Comparative 45 30 21 4 1.3 — — SAH 0.15 — — Example 21

<Manufacturing of Battery>

<Fabrication of Positive Electrode>

A composite oxide (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂) of lithium, nickel,manganese, and cobalt as the positive-electrode active material,acetylene black powder as the conductive aid, and polyvinylidenefluoride (PVDF) as the binder were mixed at a mass ratio of “100:3.5:3”to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as asolvent was added to the obtained positive electrode mixture, and theywere further mixed to prepare positive electrode mixture-containingslurry. This positive electrode mixture-containing slurry was coated onone surface of an aluminum foil having a thickness of 15 μm, which willserve as a positive electrode current collector, while adjusting thebasis weight to approximately 95.0 g/m². When the positive electrodemixture-containing slurry was coated on the aluminum foil, an uncoatedregion was formed so as to expose a part of the aluminum foil. Then,roll pressing was performed using a roll press machine until thepositive-electrode active material layer has a density of 2.50 g/cm³, sothat a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 30 mm by 50 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, carboxymethylcellulose as the binder, and styrene-butadiene latex as the binder weremixed at a mass ratio of “100:1.1:1.5” to obtain a negative electrodemixture. An appropriate amount of water was added to the obtainednegative electrode mixture, and they were mixed sufficiently to preparenegative electrode mixture-containing slurry. This negative electrodemixture-containing slurry was coated on one surface of a copper foilhaving a thickness of 10 μm while adjusting the basis weight to 60.0g/m². When the negative electrode mixture-containing slurry was coatedon the copper foil, an uncoated region was formed so as to expose a partof the copper foil. Then, roll pressing was performed using a roll pressmachine until the negative-electrode active material layer has a densityof 1.35 g/cm³, so that a negative electrode having thenegative-electrode active material layer and the negative electrodecurrent collector was obtained.

Then, this negative electrode was cut such that the negative electrodemixture layer has an area of 32 mm by 52 mm, and the exposed portion ofthe copper foil is included. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 hours at 80° C., so that alead-attached negative electrode was obtained.

<Assembly of Single-Layered Laminate-Type Battery>

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene microporousmembrane separator (having a thickness of 21 μm) while the mixture coatsurfaces of each electrode face each other, so that a laminatedelectrode structure was obtained. This laminated electrode structure washoused in an aluminum laminated sheet package having a size of 90 mm by80 mm, and vacuum drying was performed for 5 hours at 80° C. in order toremove moisture. Subsequently, each of the electrolyte solutionsdescribed above was injected into the package, and the package wassealed, so that a single-layered laminate type (pouch type) non-aqueoussecondary battery (hereinafter, simply also referred to as“single-layered laminate-type battery”) was manufactured. Thissingle-layered laminate-type battery has a design capacity value of 23mAh and a rated voltage value of 4.2 V.

<Evaluation of Single-Layered Laminate-Type Battery>

For the battery for evaluation obtained as described above, first,initial charging treatment was performed in the sequence of thefollowing chapter (1-1). Then, each battery was evaluated in thesequence of the chapter (1-2). Note that the charging/discharging wasperformed using a charging/discharging device ACD-01 (model name)produced by Asuka Electronics Co., Ltd. and a thermostatic oven PLM-63S(model name) produced by Futaba Kagaku Co., Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current.

(1-1) Initial Charging/Discharging Treatment of Single-LayeredLaminate-Type Battery

The battery was charged with a constant current of 2.3 mA correspondingto “0.1 C” to a voltage of 4.2 V by setting the battery ambienttemperature to 25° C. and was then charged with a constant voltage of4.2 V for 1.5 hours. Then, the battery was discharged with a constantcurrent of 6.9 mA corresponding to “0.3 C” to a voltage of 3.0 V.Initial efficiency was calculated by dividing the discharge capacity atthis time by the charge capacity.

(1-2) 50° C. Charging/Discharging Cycle Test for Single-LayeredLaminate-Type Battery

A cycle test was performed for the battery subjected to the initialcharging/discharging treatment using the method described in theaforementioned chapter (1-1). Note that the cycle test was initiated 3hours later after the battery ambient temperature is set to 50° C.First, the battery was charged with a constant current of 23 mAcorresponding to “1 C” to a voltage of 4.2 V, and was then charged witha constant voltage of 4.2 V for a total of 3 hours. Then, the batterywas discharged with a constant current of 23 mA to a voltage of 3.0 V.By setting one charge operation and one discharge operation as a singlecycle, the charging/discharging was performed for 100 cycles. Thedischarge capacity of the hundredth cycle was set as a capacityretention rate by assuming that the discharge capacity of the firstcycle is 100%.

(2) Measurement of Transition Metal Elution Amount

An X-ray photoelectron spectroscopy (XPS) analysis was performed tomeasure the transition metal elution amount. As an XPS analyzer, VersaProbell produced by ULVAC-PHI, Inc. was employed. As an analysiscondition, an excitation source was set to mono AlKa 15 kV×3.3 mA, ananalysis size was set to approximately 200 μm diameter, and aphotoelectron emission angle was set to 45°. In addition, themeasurement sample was disassembled from the battery before the test,and the obtained negative electrode was immersed in acetonitrile forapproximately 1 minute to wash the electrolyte solution adhering to thesample. Then, the sample was air-dried for 12 hours. The dried samplewas cut into small pieces of 3 mm square and was used as an XPS analysissample. Note that a series of operations for sample fabrication wascarried out in an argon glove box having a dew point controlled to −60°C. or lower. The sample was delivered to the XPS device without exposureto the atmosphere using a dedicated tool. A relative elementconcentration of each element was obtained using the area intensity ofeach obtained peak (C1S, O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, andCo3p) and a relative sensitivity coefficient of the device. Here, peaksplitting was performed on the Ni3p, Co3p, and Mn3p spectra observed atapproximately 40 to 80 eV to derive the area intensity, so that aNi-concentration, a Co-concentration, and a Mn-concentration wereobtained.

TABLE 20 50° C. cycle test capacity Transition metal elution retentionrate amount [ppm] [%] Mn Ni Co Example 29 89 0.3 0.2 0.2 Example 30 880.3 0.2 0.2 Comparative Example 20 71 1.2 1.0 0.3 Comparative Example 2168 1.4 1.2 0.4

As shown in Table 20, it was possible to obtain a capacity retentionrate of 75% or higher in all of the examples. In addition, in theexamples, it was possible to suppress the transition metal elutionamount of Mn, Ni, and Co to be smaller than that of the comparativeexamples.

On the basis of the examples and the comparative examples, it waspreferable that the electrolyte solution contains LiPO₂F₂ of 0.005 to 1mass %, a nitrogen-containing cyclic compound of 0.01 to 1 mass %, andcyclic acid anhydride of 0.01 to 1 mass %. In this manner, since thenitrogen-containing cyclic compound is contained, elution of metalsderived from the positive-electrode active material is suppressed.Therefore, it is possible to suppress an increase of the positiveelectrode interface resistance. Furthermore, since a certain amount ofLiPO₂F₂ and cyclic acid anhydride are contained, it is possible tosuppress a growth of the transition metal precipitated on the negativeelectrode.

On the basis of Examples 29 and 30, it was preferable that thenitrogen-containing cyclic compound is 1-methyl-1H-benzotriazole (MBTA).In this manner, the nitrogen-containing cyclic compound without N—H bondis contained, it is possible to prevent hydrogen from being released ina high-temperature cycle and suppress generation of gas.

An example of the thirty first embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 21.

Note that, in Table 21, “AcN” denotes acetonitrile, “DEC” denotesdiethyl carbonate, “EMC” denotes ethyl methyl carbonate, “DMC” denotesdimethyl carbonate, “EC” denotes ethylene carbonate, “VC” denotesvinylene carbonate, “LiPF₆” denotes lithium hexafluorophosphate,“LiN(SO₂F)₂” denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂”denotes lithium bis (trifluoromethane sulfonyl) imide, “LiPO₂F₂” denoteslithium difluorophosphate, “SAH” denotes succinic anhydride, “MAH”denotes maleic anhydride, and “PAH” denotes phthalic anhydride.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 21 Lithium salt Imide salt Additive Solvent LiPF6 Content Cyclicacid AcN DEC EMC DMC EC VC (mol/1 L (mol/1 L anhydride LiPO₂F₂ (vol %)(vol %) (vol %) (vol %) (vol %) (vol %) solvent) Type solvent) (mass %)(ppm) Example 101 49 28 0 0 21 2 0.4 LiN(SO₂F)₂ 0.9 MAH 0.15 1000Example 102 49 28 0 0 21 2 0.3 LiN(SO₂F)₂ 1.0 PAH 0.15 5000 Example 10362 0 18 0 18 2 0.6 LiN(SO₂CF₃)₂ 0.6 MAH 0.15 1000 Example 104 49 0 18 1021 2 0.3 LiN(SO₂F)₂ 1.0 SAH 0.15 1000 Example 105 47 0 30 0 21 2 0.3LiN(SO₂F)₂ 1.0 SAH 0.15 5000 Comparative 0 45 16 0 35 4 1.2 — — — —Example 101 Comparative 0 0 20 45 33 2 1.6 — — — — Example 102Comparative 0 0 20 48 27 5 1.5 — — — — Example 103 BET Postive Negative-Negative value electrode electrode electrode Positive-electrode [m2/current active current Battery type active material g] collectormaterial collector Separator Example 101 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.5 Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 102 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.6 Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 103 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.5 Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 104 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.7 Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 105 Layered laminate cellLiFePO₄ 14.6 Aluminum foil Graphite Copper foil non-woven fabricComparative Layered laminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.5Aluminum foil Graphite Copper foil Polyethylene microporous Example 101membrane Comparative Layered laminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂0.4 Aluminum foil Graphite Copper foil Polyethylene microporous Example102 membrane Comparative Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ 0.2 Aluminum foil Graphite Copper foilPolyethylene microporous Example 103 membrane

A non-aqueous secondary battery using the positive-electrode activematerial, the negative-electrode active material, the separator, and theelectrolyte solution shown in Table 21 was manufactured.

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=5/3/2 (element ratio))as the positive-electrode active material, graphite carbon powder(density: 2.26 g/cm³) having a number average particle diameter of 6.5μm and acetylene black powder (density: 1.95 g/cm³) having a numberaverage particle diameter of 48 nm as the conductive aid, andpolyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as the binder weremixed at a mass ratio of “100:4.2:1.8:4.6” to obtain a positiveelectrode mixture. N-methyl-2-pyrrolidone as a solvent was added to theobtained positive electrode mixture until a solid content of 68 mass %,and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 12.8 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 5.4 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.50 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

This multi-layered laminate-type battery has a design capacity value ofapproximately 1.5 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,initial charging/discharging treatment was performed in the followingsequence. Subsequently, the measurement of electrochemical impedancespectroscopy (−30° C.) was performed. Here, “1 C” refers to a currentvalue at which a fully charged battery is expected to be discharged inone hour at a constant current to terminate the discharge. In thefollowing description, “1 C” refers to a current value at which thedischarge operation is expected to be terminated in one hour bydischarging the battery from a full-charge state of 4.2 V to a voltageof 2.7 V at a constant current.

<Initial Charging/Discharging Treatment>

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the ambient temperature to 25° C. and was then charged witha constant voltage of 4.2 V for one hour. Then, the battery wasdischarged with a constant current of 0.2 C to a voltage of 2.7 V. Then,a sealing portion of the battery was opened, and degassing was performedinside a glove box having a dew point controlled to −60° C. or lower.After the degassing, vacuum sealing was performed under the sameenvironment.

<Measurement of Electrochemical Impedance Spectroscopy>

For the battery subjected to the initial charging/discharging treatmentusing the method described above in the chapter (2-1), the measurementof electrochemical impedance spectroscopy was performed. The measurementof electrochemical impedance spectroscopy was performed using afrequency response analyzer 1400 (model name) produced by AMETEK, Inc.and potentio-galvanostat 1470E (model name) produced by AMETEK, Inc. Theimpedance was measured from a voltage/current response signal byapplying an AC signal while changing the frequency 1000 kHz to 0.01 Hz.A value intersecting with an abscissa of a complex impedance plot(cole-cole plot) was obtained as a bulk resistance, and a value obtainedby adding the bulk resistance to a width of an arc of the high frequencyside was obtained as an internal resistance. In addition, all theresistance values were obtained using a value of a real part (abscissa).Furthermore, an amplitude of the applied AC voltage was set to “±5 mV”.Furthermore, the battery ambient temperature at the time of measurementof electrochemical impedance spectroscopy was set to −30° C., and themeasurement started after 1.5 hours from each temperature setting. Thefollowing values were calculated from such results.

TABLE 22 Bulk resistance (Ω) Bulk Bulk Internal resistance/ resistanceresistance internal (−30° C.) (−30° C.) resistance Example 101 0.06 1.300.05 Example 102 0.07 1.20 0.06 Example 103 0.07 1.37 0.05 Example 1040.06 1.18 0.05 Example 105 0.05 0.93 0.05 Comparative Example 101 0.083.72 0.02 Comparative Example 102 0.09 2.61 0.03 Comparative Example 1030.10 3.80 0.03

In Examples 101, and 103 to 105, a value obtained by dividing the bulkresistance by the internal resistance was “0.05”. In Example 102, avalue obtained by dividing the bulk resistance by the internalresistance was “0.06”. In addition, in Comparative Example 101, a valueobtained by dividing the bulk resistance by the internal resistance was“0.02”. In Comparative Example 102, a value obtained by dividing thebulk resistance by the internal resistance was “0.03”. In ComparativeExample 103, a value obtained by dividing the bulk resistance by theinternal resistance was “0.03”.

From the ranges of the examples, it was defined that the value obtainedby dividing the bulk resistance by the internal resistance in themeasurement of electrochemical impedance spectroscopy at a temperatureof −30° C. preferably has a range of 0.05 to 0.7.

An example of the thirty second embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 23. Note that, in Table 23, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salts and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 23 Lithium salt Additive Imide salt Nitrogen- Cyclic Solvent LiPF₆Content containing acid AcN DEC EMC EMC EC VC (mol/1 L) (mol/1 Lcompound anhydride LiPO₂F₂ (vol %) (vol %) (vol %) (vol %) (vol %) (vol%) solvent) Type solvent (mass %) (mass %) (ppm) Example 106 47 35 0 016 2 0.3 LiN(SO₂F)₂ 1.0 — MAH 0.2 3000 Example 107 47 0 34 0 16 3 0.5LiN(SO₂F)₂ 0.6 MBTA 0.5 PAH 0.2 3000 Example 108 37 0 40 0 21 2 0.5LiN(SO₂CF₃)₂ 0.6 MBTA 0.3 SAH 0.2 3000 Comparative 44 32 0 0 15 9 1.2 —— — SAH 2.5 — Example 104 Comparative 57 0 19 0 18 6 1.0 — — MBTA 0.01 —— Example 105 Comparative 43 0 0 35 18 4 1.2 — — MBTA 3 SAH 2.5 —Example 105 Positive Negative- Negative electrode electrode electrodePositive-electrode current active current Battery type active materialcollector material collector Separator Example 106 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 107 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 108 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 104 Layeredlaminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copperfoil Polyethylene microporous membrane Comparative Example 105 Layeredlaminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copperfoil Polyethylene microporous membrane Comparative Example 105 Layeredlaminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copperfoil Polyethylene microporous membrane

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=5/3/2 (element ratio))as the positive-electrode active material, graphite carbon powder(density: 2.26 g/cm³) having a number average particle diameter of 6.5μm and acetylene black powder (density: 1.95 g/cm³) having a numberaverage particle diameter of 48 nm as the conductive aid, andpolyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as the binder weremixed at a mass ratio of “100:4.2:1.8:4.6” to obtain a positiveelectrode mixture. N-methyl-2-pyrrolidone as a solvent was added to theobtained positive electrode mixture until a solid content of 68 mass %,and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 12.8 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 5.4 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.50 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Manufacturing of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

The multi-layered laminate-type battery has a design capacity value ofapproximately 1.5 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,initial charging/discharging treatment was performed in the followingsequence. Subsequently, the measurement of electrochemical impedancespectroscopy (−30° C.), and the 50° C. cycle test were performed. Here,“1 C” refers to a current value at which a fully charged battery isexpected to be discharged in one hour at a constant current to terminatethe discharge. In the following description, “1 C” refers to a currentvalue at which the discharge operation is expected to be terminated inone hour by discharging the battery from a full-charge state of 4.2 V toa voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the ambient temperature to 25° C. and was then charged witha constant voltage of 4.2 V for one hour. Note that, for themulti-layered laminate-type battery having a designated aging condition,the initial charging was performed as described in the condition ofTable 24. Then, the battery was discharged with a constant current of0.2 C to a voltage of 2.7 V. Then, a sealing portion of the battery wasopened, and degassing was performed inside a glove box having a dewpoint controlled to −60° C. or lower. After the degassing, vacuumsealing was performed under the same environment.

<50° C. Charging/Discharging Cycle Test>

A cycle test was performed for the battery subjected to the initialcharging/discharging treatment using the method described in theaforementioned chapter (2-1). Note that the cycle test was initiated 3hours later after the battery ambient temperature is set to 50° C.First, the battery was charged with a constant current of 1.5 Acorresponding to “1 C” to a voltage of 4.2 V, and was then charged witha constant voltage of 4.2 V for a total of 3 hours. Then, the batterywas discharged with a constant current of 1.5 A to a voltage of 2.7 V.By setting one charge operation and one discharge operation as a singlecycle, the charging/discharging was performed for 200 cycles. Thedischarge capacity of the two hundredth cycle was set as a capacityretention rate by assuming that the discharge capacity of the firstcycle is 100%.

<Measurement of Electrochemical Impedance Spectroscopy>

For the battery subjected to the initial charging/discharging treatmentusing the method described above in the chapter (2-1), the measurementof electrochemical impedance spectroscopy was performed. The measurementof electrochemical impedance spectroscopy was performed using afrequency response analyzer 1400 (model name) produced by AMETEK, Inc.and potentio-galvanostat 1470E (model name) produced by AMETEK, Inc. Theimpedance was measured from a voltage/current response signal byapplying an AC signal while changing the frequency 1000 kHz to 0.01 Hz.A value intersecting with an abscissa of a complex impedance plot(cole-cole plot) was obtained as a bulk resistance, and a value obtainedby adding the bulk resistance to a width of an arc of the high frequencyside was obtained as an internal resistance. In addition, all theresistance values were obtained using a value of a real part (abscissa).Furthermore, an amplitude of the applied AC voltage was set to “±5 mV”.Furthermore, the battery ambient temperature at the time of measurementof electrochemical impedance spectroscopy was set to −30° C., and themeasurement started after 1.5 hours from each temperature setting. Thefollowing values were calculated from such results. Table 25 shows theexperimental results.

TABLE 24 Aging Aging voltage temperature Aging [V] [° C.] time [h]Example 106 3.5 40.0 36 Example 107 2.8 50.0 48 Example 108 3.1 55.0  6Comparative Example 104 — — — Comparative Example 105 — — — ComparativeExample 106 3.8 85.0 12

TABLE 25 Capacity Bulk resistance (Ω) retention rate —N═, —NH₄, —N═O,Bulk Internal Bulk in 50° C. cycle C—N—N—C, —(NO₃) resistance resistanceresistance/internal test [atomic %] (−30° C.) (−30° C.) resistance [%]Example 106 5.5 0.06 1.30 0.05 80 Example 107 13.4 0.06 1.25 0.05 83Example 108 7.9 0.07 1.29 0.05 84 Comparative Example 104 0.2 0.07 2.590.03 73 Comparative Example 105 0.4 0.08 2.10 0.04 75 ComparativeExample 106 24.5 0.10 4.98 0.02 39

On the basis of this experimental result, it was preferable that thenon-aqueous secondary battery contains a compound having at least onefunctional group selected from a group consisting of —N═, —NH₄, —N═O,—NH—NH—, and (NO₃)—, and the value obtained by dividing the bulkresistance by the internal resistance value in the measurement ofelectrochemical impedance spectroscopy at a temperature of −30° C. has arange of 0.05 to 0.7.

In this example, it was recognized that a capacity retention rate of 80%or higher can be obtained in the 50° C. cycle test.

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the positive electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKα 15 kVx3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. Note that a series of operations for sample fabricationwas carried out in an argon glove box (a dew point of −60° C. or lower).The sample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each obtained peak(C1S, O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and arelative sensitivity coefficient of the device. Here, peak splitting wasperformed on the N1s spectrum observed at approximately 394 to 408 eV toderive the area intensity, so that an N-concentration was obtained. Inaddition, within the aforementioned peak range, the peaks observed atapproximately 399 eV to 400 eV have —NH₄, —NH—NH—, (NO₃)—, and N═Obonds. The “atomic %” shown in Table 25 refers to an oxygenconcentration in atomic % when peak splitting of the photoelectronspectrum is performed.

In this example, it was defined that the positive electrode of thebattery preferably contains a compound containing at least functionalgroup selected from a group consisting of —N═, —NH₄, —N═O, —NH—NH—, and(NO₃)— by 0.5 to 20 atomic %. This is based on the value obtained bydividing the bulk resistance by the internal resistance and the resultof the 50° C. cycle test in Examples 106 to 108 and Comparative Examples104 to 106.

On the basis of the experimental results of Examples 106 to 108, it waspreferable that the positive electrode of the battery contains acompound containing at least one functional group selected from a groupconsisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)— by 0.5 to 20 atomic%, and there is a thermal history of 40° C. or higher at the initialcharging. In this manner, if the component of the positive electrodefilm has a compound containing at least one functional group selectedfrom a group consisting of —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)—, it ispossible to suppress elution of metal derived from thepositive-electrode active material and improve a cycle life and safety.

Examples of the thirty third and thirty fifth embodiment will now bedescribed.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 26. Note that, in Table 26, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salts and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 26 Lithium salt Additive Imide salt Nitrogen- Cyclic Solvent LiPF₆Content containing acid AcN DEC EMC DMC EC VC (mol/1 L (mol/1 L compoundanhydride LiPO₂F₂ (vol %) (vol %) (vol %) (vol %) (vol %) (vol %)solvent) Type solvent) (mass %) (mass %) (ppm) Example 109 41 30 0 0 272 0.4 LiN(SO₂F)₂ 1.0 — PAH 0.2 3000 Example 110 60 0 22 0 15 3 0.6LiN(SO₂CF₃)₂ 0.6 MBTA 0.2 MAH 0.15 1000 Example 111 51 0 22 0 25 2 0.3LiN(SO₂F)₂ 1.0 — SAH 0.3 3000 Comparative 0 0 67 0 30 3 1.0 — — — — —Example 107 Comparative 0 72 0 0 25 3 1.3 — — — — — Example 108Comparative 0 39 0 30 28 3 1.2 — — — — — Example 109 Negative- Negativeelectrode electrode Positive-electrode Positive electrode active currentBattery type active material current collector material collectorSeparator Example 109 Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂Aluminum foil Graphite Copper foil Polyethylene microporous membraneExample 110 Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane Example 111Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane ComparativeExample 107 Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane ComparativeExample 108 Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane ComparativeExample 109 Layered laminate cell LiN_(i0.5)Mn_(0.3)Co_(0.2)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=5/3/2 (element ratio))as the positive-electrode active material, graphite carbon powder(density: 2.26 g/cm³) having a number average particle diameter of 6.5μm and acetylene black powder (density: 1.95 g/cm³) having a numberaverage particle diameter of 48 nm as the conductive aid, andpolyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as the binder weremixed at a mass ratio of “100:4.2:1.8:4.6” to obtain a positiveelectrode mixture. N-methyl-2-pyrrolidone as a solvent was added to theobtained positive electrode mixture until a solid content of 68 mass %,and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 12.8 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 5.4 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.50 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

The multi-layered laminate-type battery has a design capacity value ofapproximately 1.5 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,initial charging/discharging treatment was performed in the followingsequence. Subsequently, the measurement of electrochemical impedancespectroscopy (−30° C.) and the 50° C. cycle test were performed. Here,“1 C” refers to a current value at which a fully charged battery isexpected to be discharged in one hour at a constant current to terminatethe discharge. In the following description, “1 C” refers to a currentvalue at which the discharge operation is expected to be terminated inone hour by discharging the battery from a full-charge state of 4.2 V toa voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-Type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the ambient temperature to 25° C. and was then charged witha constant voltage of 4.2 V for one hour. Then, the battery wasdischarged with a constant current of 0.2 C to a voltage of 2.7 V. Then,a sealing portion of the battery was opened, and degassing was performedinside a glove box having a dew point controlled to −60° C. or lower.After the degassing, vacuum sealing was performed under the sameenvironment.

<Measurement of Electrochemical Impedance Spectroscopy>

For the battery subjected to the initial charging/discharging treatmentusing the method described above in the chapter (2-1), the measurementof electrochemical impedance spectroscopy was performed. The measurementof electrochemical impedance spectroscopy was performed using afrequency response analyzer 1400 (model name) produced by AMETEK, Inc.and potentio-galvanostat 1470E (model name) produced by AMETEK, Inc. Theimpedance was measured from a voltage/current response signal byapplying an AC signal while changing the frequency 1000 kHz to 0.01 Hz.A value intersecting with an abscissa of a complex impedance plot(cole-cole plot) was obtained as a bulk resistance. In addition, all theresistance values were obtained using a value of a real part (abscissa).Furthermore, an amplitude of the applied AC voltage was set to “±5 mV”.Moreover, the battery ambient temperature at the time of measurement ofelectrochemical impedance spectroscopy was set to 25° C. and −30° C.,and the measurement started after 1.5 hours from each temperaturesetting. The following values of Table 27 were calculated from suchresults.

TABLE 27 Bulk Bulk resistance (Ω) resistance (Ω) (25° C.) (−30° C.)Example 109 0.021 0.06 Example 110 0.023 0.07 Example 111 0.020 0.06Comparative Example 107 0.031 0.09 Comparative Example 108 0.033 0.10Comparative Example 109 0.030 0.11

On the basis of this experimental result, it was preferable that thenegative-electrode active material layer contains a compound containingat least one selected from a group consisting of imide salt and (SO₄)²⁻,the imide salt is at least one selected from a group consisting oflithium salt and onium salt, and the non-aqueous secondary battery has abulk resistance of 0.025 ohm or smaller at a temperature of 25° C. inthe measurement of electrochemical impedance spectroscopy. As a result,a decomposition product derived from the imide salt forms a film on thenegative-electrode active material layer, so that it is possible toimprove durability of acetonitrile. Furthermore, since the bulkresistance at a temperature of 25° C. is 0.025 ohm or smaller, it ispossible to obtain both high output power and high durability.

On the basis of the examples and the comparative examples, it ispreferable that the negative-electrode active material layer contains acompound containing at least one selected from a group consisting ofimide salt and (SO₄)²⁻, the imide salt is at least one selected from agroup consisting of lithium salt and onium salt, and the non-aqueoussecondary battery has a bulk resistance of 0.07 ohm or smaller at atemperature of −30° C. in the measurement of electrochemical impedancespectroscopy. As a result, a decomposition product derived from theimide salt forms a film on the negative-electrode active material layer,so that it is possible to obtain a film having a small interfaceresistance. Furthermore, since the bulk resistance at a temperature of−30° C. is 0.07 ohm or smaller, it is possible to provide a secondarybattery having very excellent balance between a lithium ion diffusionreaction and an interface reaction and high low-temperature performance.

On the basis of Examples 109 to 111, it was preferable that a filmformed of LiPO₂F₂ and cyclic acid anhydride is formed on the surface ofthe negative-electrode active material. As a result, it is possible tosuppress an increase of the resistance in a low temperature range.

An example of the thirty fourth embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 28. Note that, in Table 28, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “EC” denotes ethylene carbonate, “VC” denotes vinylenecarbonate, “LiPF₆” denotes lithium hexafluorophosphate, “LiN(SO₂F)₂”denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denoteslithium bis (trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, and “PAH” denotes phthalic anhydride.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 28 Lithium salt Additive Imide salt Cyclic Solvent LiPF₆ Contentacid AcN DEC EMC EC VC (mol/1 L (mol/1 L anhydride LiPO₂F₂ (vol %) (vol%) (vol %) (vol %) (vol %) solvent) Type solvent) (mass %) (ppm) Batterytype Example 112 45 35 0 18 2 0.3 LiN(SO₂F)₂ 1.0 SAH 0.2 5000 Layeredlaminate cell Example 113 46 0 35 17 2 0.5 LiN(SO₂F)₂ 0.6 MAH 0.15 5000Layered laminate cell Example 114 35 0 40 23 2 0.5 LiN(SO₂CF₃)₂ 0.6 PAH0.5 1000 Layered laminate cell Comparative 35 32 0 24 9 1.2 — — SAH 3.0— Layered laminate cell Example 110 Comparative 46 0 23 20 11 1.5 — —SAH 2.5 — Layered laminate cell Example 111 Positive Negative electrodeelectrode Positive-electrode current Negative-electrode active currentactive material collector material collector Separator Example 112LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 113LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite and Li₂O powder ofCopper foil Polyethylene microporous 0.05 mass % mixing membrane Example114 LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 110LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 111LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane

A non-aqueous secondary battery using the positive-electrode activematerial, the negative-electrode active material, the separator, and theelectrolyte solution shown in Table 28 was manufactured.

<Manufacturing of Non-Aqueous Electrolyte Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=5/3/2 (element ratio))as the positive-electrode active material, graphite carbon powder(density: 2.26 g/cm³) having a number average particle diameter of 6.5μm and acetylene black powder (density: 1.95 g/cm³) having a numberaverage particle diameter of 48 nm as the conductive aid, andpolyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as the binder weremixed at a mass ratio of “100:4.2:1.8:4.6” to obtain a positiveelectrode mixture. N-methyl-2-pyrrolidone as a solvent was added to theobtained positive electrode mixture until a solid content of 68 mass %,and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 12.8 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. Note that the Li₂O powder mixture coat wasobtained by mixing Li₂O powder (density: 2.01 g/cm³) to match apredetermined amount described in the tables relative to a solid contentmass of 100% of the slurry subjected to the slurry adjustment. Thisnegative electrode mixture-containing slurry was coated on both surfacesof a copper foil having a thickness of 10 μm and a width of 200 mm,which will serve as a negative electrode current collector, using adoctor blade method while adjusting the basis weight of one surface to5.4 mg/cm², and the solvent was dried and removed. When the negativeelectrode mixture-containing slurry was coated on the copper foil, anuncoated region was formed so as to expose a part of the copper foil.Then, roll pressing was performed using a roll press machine to anactual electrode density of 1.50 g/cm³, and a negative electrode havingthe negative-electrode active material layer and the negative electrodecurrent collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

The multi-layered laminate-type battery has a design capacity value ofapproximately 1.5 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,initial charging/discharging treatment was performed in the followingsequence. Subsequently, the measurement of electrochemical impedancespectroscopy (−30° C.) and the 50° C. cycle test were performed. Here,“1 C” refers to a current value at which a fully charged battery isexpected to be discharged in one hour at a constant current to terminatethe discharge. In the following description, “1 C” refers to a currentvalue at which the discharge operation is expected to be terminated inone hour by discharging the battery from a full-charge state of 4.2 V toa voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-Type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the multi-layered laminate-type battery ambient temperatureto 25° C. and was then charged with a constant voltage of 4.2 V for onehour. Then, the battery was discharged with a constant current of 0.2 Cto a voltage of 2.7 V. Then, a sealing portion of the battery wasopened, and degassing was performed inside a glove box having a dewpoint controlled to −60° C. or lower. After the degassing, vacuumsealing was performed under the same environment.

<Measurement of Electrochemical Impedance Spectroscopy>

For the battery subjected to the initial charging/discharging treatmentusing the method described above in the chapter (2-1), the measurementof electrochemical impedance spectroscopy was performed. The measurementof electrochemical impedance spectroscopy was performed using afrequency response analyzer 1400 (model name) produced by AMETEK, Inc.and potentio-galvanostat 1470E (model name) produced by AMETEK, Inc. Theimpedance was measured from a voltage/current response signal byapplying an AC signal while changing the frequency 1000 kHz to 0.01 Hz.A value intersecting with an abscissa of a complex impedance plot(cole-cole plot) was obtained as a bulk resistance, and a value obtainedby adding the bulk resistance to a straight line length of an arcintersecting with the abscissa of the high frequency side was obtainedas an internal resistance. In addition, all the resistance values wereobtained using a value of a real part (abscissa). An amplitude of theapplied AC voltage was set to “±5 mV”. Furthermore, the battery ambienttemperature at the time of measurement of electrochemical impedancespectroscopy was set to −30° C., and the measurement started after 1.5hours from each temperature setting. The following values werecalculated from such results. In addition, the values of the followingTable 29 were calculated from such results.

TABLE 29 Bulk resistance (Ω) Organic acid or Bulk Internal Bulk saltthereof, Li₂O resistance resistance resistance/internal [atomic %] (−30°C.) (−30° C.) resistance Example 112 15.1 0.06 1.31 0.05 Example 11324.0 0.06 1.30 0.05 Example 114 21.4 0.06 1.29 0.05 Comparative Example110 39.0 0.08 2.65 0.03 Comparative Example 111 40.2 0.08 3.24 0.02

In Examples 112 to 114, the value obtained by dividing the bulkresistance by the internal resistance was “0.05”. From the ranges of theexamples, it was defined that the value obtained by dividing the bulkresistance by the internal resistance at a temperature of −30° C. in themeasurement of electrochemical impedance spectroscopy preferably has arange of 0.05 to 0.7. In addition, it was preferable that the batterycontains at least one compound selected from a group consisting oforganic acid (such as acetic acid, oxalic acid, and formic acid), saltthereof, acid anhydride, and Li₂O.

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the negative electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKa 15 kV×3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. Note that a series of operations for sample fabricationwas carried out in an argon glove box (a dew point of −60° C. or lower).The sample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each peak (C1s,O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and a relativesensitivity coefficient of the device. Here, peak splitting wasperformed on the O1s spectrum observed at approximately 524 to 540 eV toderive the area intensity, so that an O-concentration was obtained.Within the aforementioned peak range, the peaks observed atapproximately 528 eV have Li₂O, and the peaks observed at approximately530 to 535 eV have an organic product or salt thereof. The “atomic %”shown in Table 29 refers to an oxygen concentration in atomic % whenpeak splitting of the photoelectron spectrum is performed.

On the basis of the examples and the comparative examples, it waspreferable that the negative electrode of the battery contains at leastone compound selected from a group consisting of organic acid (such asacetic acid, oxalic acid, and formic acid), salt thereof, acidanhydride, and Li₂O by 1 to 35 atomic %. As a result, a negativeelectrode SEI having excellent ionic conductivity is formed, so that itis possible to suppress an increase of the internal resistance of thebattery using the acetonitrile electrolytic solution and improve cycleperformance.

On the basis of Examples 112 to 114, it was preferable that the negativeelectrode of the battery contains at least one compound selected from agroup consisting of organic acid (such as acetic acid, oxalic acid, andformic acid), salt thereof, acid anhydride, and Li₂O by 10 to 25 atomic%. As a result, an SEI having high acetonitrile resistance is formed, sothat it is possible to reduce the addition amount of VC in theacetonitrile electrolytic solution. As a result, it is possible tosuppress an increase of the internal resistance and improve output powerperformance.

An example of the thirty sixth embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 30. Note that, in Table 30, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 30 Lithium salt Solvent Imide salt Additive AcN DEC EMC DMC LiPF₆Content Nitrogen-containing Cyclic acid (vol (vol (vol (vol EC VC (mol/1L) (mol/1 L compound anhydride LiPO₂F₂ %) %) %) %) (vol %) (vol %)solvent) Type solvent (mass %) (mass %) (ppm) Example 115 45 35 0 0 16 40.3 LiN(SO₂F)₂ 1.3 — SAH 0.15 3000 Example 116 45 0 35 0 16 4 0.4LiN(SO₂F)₂ 1.0 MBTA 0.2 SAH 0.3 1500 Example 117 35 0 40 0 21 4 0.4LiN(SO₂F)₂ 0.9 MBTA 0.1 MAH 0.15 1500 Example 118 65 0 0 6 22 7 0.6LiN(SO₂CF₃)₂ 0.6 Methyl PAH 0.2 500 succinonitrile 0.2 Example 119 45 300 0 23 2 1.0 LiN(SO₂F)₂ — MBTA 0.3 PAH 0.2 1500 Example 120 50 0 30 0 182 0.3 LiN(SO₂F)₂ 1.0 — SAH 0.2 3000 Comparative 47 42 0 0 0 11 1.3LiN(SO₂F)₂ 0.03 — MAH 0.01 — Example 112 Comparative 47 49 0 0 0 4 1.3LiN(SO₂CF₃)₂ 0.03 — SAH 0.05 — Example 113 Comparative 47 49 0 0 0 4 0.3LiN(SO₂CF₃)₂ 1 MBTA2.5 SAH 2.5 — Example 114 Negative- Negative Positiveelectrode electrode Positive-electrode active eletrode current activecurrent Battery type material collector material collector SeparatorExample 115 Coin (CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane Example 116 Coin(CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 117 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 118 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 119 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 120 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 112 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 113 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Example 114 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane

<Manufacturing of Non-aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture. N-methyl-2-pyrrolidone as a solvent wasadded to the obtained positive electrode mixture until a solid contentof 68 mass %, and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on one surface of an aluminum foil having a thicknessof 20 μm and a width of 200 mm, which will serve as a positive electrodecurrent collector, using a doctor blade method while adjusting the basisweight to 12.0 mg/cm², and the solvent was dried and removed. Then, rollpressing was performed using a roll press machine to an actual electrodedensity of 2.80 g/cm³, so that a positive electrode having thepositive-electrode active material layer and the positive electrodecurrent collector was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. Note that the Li₂O powder mixture coat wasobtained by mixing Li₂O powder (density: 2.01 g/cm³) to match apredetermined amount described in the tables relative to a solid contentmass of 100% of the slurry subjected to the slurry adjustment. Thisnegative electrode mixture-containing slurry was coated on one surfaceof a copper foil having a thickness of 10 μm and a width of 200 mm,which will serve as a negative electrode current collector, using adoctor blade method while adjusting the basis weight to 5.3 mg/cm², andthe solvent was dried and removed. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 1.30 g/cm³,and a negative electrode having the negative-electrode active materiallayer and the negative electrode current collector was obtained.

(1-3) Fabrication of Coin Type Non-Aqueous Secondary Battery

A polypropylene gasket was set on a CR2032 type battery casing(SUS304/Al-cladding), and the positive electrode obtained as describedabove was punched in a disk shape having a diameter of 16 mm and was seton a center of the gasket while the positive-electrode active materiallayer faces upward. A polyethylene microporous membrane punched in adisk shape having a diameter of 19 mm was set thereon, and anelectrolyte solution was injected by 100 μL. Then, the negativeelectrode obtained as described above and punched in a disk shape havinga diameter of 16 mm was set thereon while the negative-electrode activematerial layer faces downward. In addition, a spacer and a spring wereset, and then a battery cap was fitted and crimped with a caulkingmachine. The overflowing electrolyte solution was wiped out with a wastecloth. The assembly was maintained at a temperature of 25° C. for 24hours to fully adapt the electrolyte solution to the stacking component,so that a coin type non-aqueous secondary battery was obtained.

<Evaluation of Coin Type Non-Aqueous Secondary Battery>

For the battery for evaluation obtained as described above, initialcharging treatment was performed in a respective sequence described inthe examples and the comparative examples. Then, each battery wasevaluated in the sequence of the chapters (2-1) and (2-2). Note that thecharging/discharging was performed using a charging/discharging deviceACD-01 (model name) produced by Asuka Electronics Co., Ltd. and athermostatic oven PLM-63S (model name) produced by Futaba Kagaku Co.,Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current.

(2-1) 85° C. Full-Charge Storage Test for Coin Type Non-AqueousSecondary Battery

The battery subjected to the initial charging/discharging treatment(aging treatment of the initial discharging will be described in eachexample or comparative example) was charged with a constant current of 3mA corresponding to “1 C” to a voltage of 4.2 V by setting the batteryambient temperature to 25° C., and was then charged with a constantvoltage of 4.2 V for a total of 3 hours. Then, this non-aqueoussecondary battery was stored in a thermostatic oven at a temperature of85° C. for 4 hours. Then, the battery ambient temperature was recoveredto 25° C.

(2-2) Output Power Test for Coin Type Non-Aqueous Secondary Battery

The battery subjected to the 85° C. full-charge storage test asdescribed above in the chapter (2-1) was charged with a constant currentof 3 mA corresponding to “1 C” to a voltage of 4.2 V by setting thebattery ambient temperature to 25° C., and was then charged with aconstant voltage of 4.2 V for a total of 3 hours. Then, the battery wasdischarged with a current value of 3 mA corresponding to “1 C” to avoltage of 3.0 V. Then, the charging/discharging was performed asdescribed above by changing the current value for the constant currentdischarging to 15 mA corresponding to “5 C”, and the following capacityretention rate was calculated.Capacity Retention Rate=(capacity for “5 C” discharge/capacity for “1 C”discharge)×100[%]

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the positive electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKα 15 kV×3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. Note that a series of operations for sample fabricationwas carried out in an argon glove box (a dew point of −60° C. or lower).The sample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each peak (C1s,O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and a relativesensitivity coefficient of the device. Here, peak splitting wasperformed on the N1s spectrum observed at approximately 394 to 408 eV toderive the area intensity and obtain the N-concentration. Within theaforementioned peak range, the peaks observed at approximately 399 to402 eV have —NH₄, —NH—NH—, (NO₃)—, and —N═O bonds.

Note that the following Table 31 shows the aging conditions, and Table32 shows the experimental results.

TABLE 31 Aging voltage Aging Aging [V] temperature [° C.] time [h]Example 115 2.8 55.0 6 Example 116 2.8 45.0 72 Example 117 3.0 55.0 6Example 118 3.0 60.0 6 Example 119 3.3 55.0 24 Example 120 3.2 50.0 48Comparative Example 112 — — — Comparative Example 113 2.8 25.0 72Comparative Example 114 4.2 85.0 24

TABLE 32 Capacity retention rate —N═, —NH₄, [%] in ouput ——N═O, C—N—N—C,power test after —(NO₃) storage test of [atomic %] 85° C. and 4 hExample 115 5.2 79 Example 116 10.1 78 Example 117 7.6 77 Example 1184.4 78 Example 119 12.1 79 Example 120 4.9 77 Comparative 0.4 63 Example112 Comparative 0.3 62 Example 113 Comparative 20.5 41 Example 114

On the basis of this experimental result, it was preferable that thenon-aqueous secondary battery contains a compound containing at leastone functional group selected from a group consisting of —N═, —NH₄,—N═O, —NH—NH—, and (NO₃)—, and the non-aqueous secondary battery has acapacity retention rate of 70% or higher, where the capacity retentionrate is calculated by dividing a 5 C discharge capacity by a 1 Cdischarge capacity after a storage test for 4 hours at 85° C.

It was recognized that resistance of a thermal history can be obtainedbecause an increase of the internal resistance on the positive electrodeinterface is suppressed by controlling the aging condition at the timeof the initial charging.

Specifically, on the basis of the examples and the comparative examples,it was preferable that a nitrogen-containing compound is contained, andaging is performed at a voltage of 3.5 V or lower at the time of theinitial charging. As a result, before ionization of the transition metalderived from the positive-electrode active material, the compoundcontaining at least a functional group selected from a group consistingof —N═, —NH₄, —N═O, —NH—NH—, and (NO₃)— can protect the surface of thepositive electrode. As a result, it is possible to suppress an increaseof the internal resistance over time caused by a thermal history.

In Examples 115 to 120, it was preferable that the aging temperature isset to 35° C. or higher and lower than 60° C. By applying a thermalhistory at a temperature lower than 60° C., the protective film caninactivate the activation point of the positive electrode surface at anearly stage and suppress an increase of the internal resistance under ahigh temperature condition.

An example of the thirty seventh embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 33. Note that, in Table 33, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 33 Lithium salt Additive Solvent Imide salt Nitrogen- EMC LiPF₆Content containing Cyclic acid AcN DEC (vol DMC EC VC (mol/1 L) (mol/1 Lcompound anhydride LiPO₂F₂ (vol %) (vol %) %) (vol %) (vol %) (vol %)solvent) Type solvent) (mass %) (mass %) (ppm) Example 121 40 37 0 0 194 0.5 LiN(SO₂F)₂ 1.0 — SAH 0.15 500 Example 122 45 5 30 0 15 5 0.6LiN(SO₂CF₃)₂ 0.6 MBTA 0.2 MAH 0.15 1000 Example 123 29 0 35 11 21 4 0.3LiN(SO₂F)₂ 1.0 — MAH 0.15 3000 Example 124 65 0 0 9 20 6 0.5LiN(SO₂CF₃)₂ 0.2 — PAH 0.5 100 Example 125 43 28 0 0 27 2 0.4 LiN(SO₂F)₂0.6 — SAH 0.2 1000 Example 126 51 0 27 0 19 3 0.4 LiN(SO2F)₂ 0.7 — — 500Comparative 47 41 0 0 0 12 1.2 — — — MAH 3.3 — Example 115 Comparative47 45 0 0 0 8 1.2 — — — SAH 5.0 — Example 116 Comparative 47 43 0 0 0 100.5 LiN(SO₂CF₃)₂ 0.8 — PAH 2.5 — Example 117 Negative Positive electrodePositive-electrode active eletrode Negative-electrode active currentBattery type material current collector material collector SeparatorExample 121 Coin (CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane Example 122 Coin(CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite and Li2OCopper foil Polyethylene microporous powder of 0.05 mass % membranemixing Example 123 Coin (CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane Example 124Coin (CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copperfoil Polyethylene microporous membrane Example 125 Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite and Li₂O Copper foilPolyethylene microporous powder of 0.01 mass % membrane mixing Example126 Coin (CR2032) LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil GraphiteCopper foil Polyethylene microporous membrane Comparative Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous Example 115 membrane Comparative Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous Example 116 membrane Comparative Coin (CR2032)LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous Example 117 membrane

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture. N-methyl-2-pyrrolidone as a solvent wasadded to the obtained positive electrode mixture until a solid contentof 68 mass %, and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on one surface of an aluminum foil having a thicknessof 20 μm and a width of 200 mm, which will serve as a positive electrodecurrent collector, using a doctor blade method while adjusting the basisweight to 12.0 mg/cm², and the solvent was dried and removed. Then, rollpressing was performed using a roll press machine to an actual electrodedensity of 2.80 g/cm³, so that a positive electrode having thepositive-electrode active material layer and the positive electrodecurrent collector was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on one surface of a copper foil having a thickness of10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight to 5.3 mg/cm², and the solvent was dried and removed. Then, rollpressing was performed using a roll press machine to an actual electrodedensity of 1.30 g/cm³, and a negative electrode having thenegative-electrode active material layer and the negative electrodecurrent collector was obtained.

(1-3) Fabrication of Coin Type Non-Aqueous Secondary Battery

A polypropylene gasket was set on a CR2032 type battery casing(SUS304/Al-cladding), and the positive electrode obtained as describedabove was punched in a disk shape having a diameter of 16 mm and was seton a center of the gasket while the positive-electrode active materiallayer faces upward. A polyethylene microporous membrane punched in adisk shape having a diameter of 19 mm was set thereon, and anelectrolyte solution was injected by 100 μL. Then, the negativeelectrode obtained as described above and punched in a disk shape havinga diameter of 16 mm was set thereon while the negative-electrode activematerial layer faces downward. In addition, a spacer and a spring wereset, and then a battery cap was fitted and crimped with a caulkingmachine. The overflowing electrolyte solution was wiped out with a wastecloth. The assembly was maintained at a temperature of 25° C. for 24hours to fully adapt the electrolyte solution to the stacking component,so that a coin type non-aqueous secondary battery was obtained.

<Evaluation of Coin Type Non-Aqueous Secondary Battery>

For the battery for evaluation obtained as described above, initialcharging treatment was performed in a respective sequence described inthe examples and the comparative examples. Then, each battery wasevaluated in the sequence of the chapters (2-1) and (2-2). Note that thecharging/discharging was performed using a charging/discharging deviceACD-01 (model name) produced by Asuka Electronics Co., Ltd. and athermostatic oven PLM-63S (model name) produced by Futaba Kagaku Co.,Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current.

(2-1) 85° C. Full-Charge Storage Test for Coin Type Non-AqueousSecondary Battery

The battery subjected to the initial charging/discharging treatment(aging treatment of the initial discharging will be described in eachexample or comparative example) was charged with a constant current of 3mA corresponding to “1 C” to a voltage of 4.2 V by setting the batteryambient temperature to 25° C., and was then charged with a constantvoltage of 4.2 V for a total of 3 hours. Then, this non-aqueoussecondary battery was stored in a thermostatic oven at a temperature of85° C. for 4 hours. Then, the battery ambient temperature was recoveredto 25° C.

(2-2) Output Power Test for Coin Type Non-Aqueous Secondary Battery

The battery subjected to the 85° C. full-charge storage test asdescribed above in the chapter (2-1) was charged with a constant currentof 3 mA corresponding to “1 C” to a voltage of 4.2 V by setting thebattery ambient temperature to 25° C., and was then charged with aconstant voltage of 4.2 V for a total of 3 hours. Then, the battery wasdischarged with a current value of 3 mA corresponding to “1 C” to avoltage of 3.0 V. Then, the charging/discharging was performed asdescribed above by changing the current value for the constant currentdischarging to 15 mA corresponding to “5 C”, and the following capacityretention rate was calculated.Capacity Retention Rate=(capacity for “5 C” discharge/capacity for “1 C”discharge)×100[%]

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the negative electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKα 15 kV×3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. A series of operations for sample fabrication wascarried out in an argon glove box (a dew point of −60° C. or lower). Thesample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each peak (C1s,O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and a relativesensitivity coefficient of the device. Here, peak splitting wasperformed on the Ols spectrum observed at approximately 524 to 540 eV toderive the area intensity and obtain the 0-concentration. Within theaforementioned peak range, the peaks observed at approximately 528 eVhave Li₂O, and the peaks observed at approximately 530 to 535 eV have anorganic product or salt thereof.

Note that the following Table 34 shows the aging conditions, and Table35 shows the experimental results.

TABLE 34 Aging Aging voltage temperature Aging [V] [° C.] time [h]Example 121 2.8 55.0 6 Example 122 2.8 45.0 72 Example 123 3.0 55.0 6Example 124 3.0 60.0 6 Example 125 3.3 55.0 24 Example 126 3.2 50.0 48Comparative Example 115 — — — Comparative Example 116 2.8 25.0 72Comparative Example 117 4.2 85.0 24

TABLE 35 Capacity retention rate [%] in ouput Organic acid or power testafter salt thereof, Li2O storage test of 85° C. [atomic %] and 4 hExample 121 15.1 82 Example 122 22.3 79 Example 123 23.6 75 Example 12426.9 80 Example 125 18.4 77 Example 126 17.9 75 Comparative Example 11538.0 55 Comparative Example 116 39.5 38 Comparative Example 117 41.1 49

On the basis of this experimental result, it was preferable that thenon-aqueous secondary battery contains at least a compound selected froma group consisting of organic acid, salt thereof, acid anhydride, andLi₂O, the organic acid contains at least one selected from a groupconsisting of acetic acid, oxalic acid, and formic acid, and thenon-aqueous secondary battery has a capacity retention rate of 70% orhigher, where the capacity retention rate is calculated by dividing a 5C discharge capacity by a 1 C discharge capacity after a storage testfor 4 hours at 85° C.

It was recognized that resistance of a thermal history can be obtainedbecause an increase of the internal resistance is suppressed bycontrolling the aging condition at the time of the initial charging.

Specifically, on the basis of the examples and the comparative examples,it was preferable that cyclic acid anhydride is contained, and aging isperformed at a voltage of 3.5 V or lower at the time of the initialcharging. As a result, since the negative electrode SEI film contains atleast a compound selected from a group consisting of organic acid (suchas acetic acid, oxalic acid, or formic acid), salt thereof, acidanhydride, and Li₂O, it is possible to suppress an increase of theinternal resistance over time caused by a thermal history.

In Examples 121 to 126, it was preferable that the aging temperature isset to 35° C. or higher and lower than 60° C. It is possible to suppressthermal decomposition of LiPF₆ generated at a temperature of 60° C. orhigher.

An example of the thirty eighth embodiment will now be described.

<Preparation of Electrolyte Solution>

Example 127

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:36:16:3” to obtain a mixed solvent. Inaddition, succinic anhydride (SAH) was dissolved in this mixed solventfinally up to 0.18 mass % as an electrolyte solution.

Then, LiPF₆ of 0.5 mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂)of 1.0 mol, and LiPO₂F₂ of 3000 ppm were added per 1 L of the mixedsolvent, so as to obtain an electrolyte solution of Example 127. In thiscase, the electrolyte solution was produced by receiving only thethermal history of 50° C. or lower. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved.

Example 128

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “55:25:16:4” to obtain a mixed solvent. Inaddition, succinic anhydride (SAH) was dissolved in this mixed solventfinally up to 0.12 mass % as an electrolyte solution. Furthermore,1-methyl-1H-benzotriazole (MBTA) was dissolved in this mixed solventfinally up to 0.3 mass % as an electrolyte solution. In this case, thetemperature of the mixed liquid was 30° C. Then, LiPF₆ of 0.3 mol,lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.7 mol, and LiPO₂F₂of 3000 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 128 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved.

Example 129

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “31:45:21:3” to obtain a mixed solvent. Inaddition, maleic anhydride (MAH) was dissolved in this mixed solventfinally up to 0.1 mass % as an electrolyte solution. Then, LiPF₆ of 0.5mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.6 mol, andLiPO₂F₂ of 5000 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 129 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved.

Example 130

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “65:10:22:3” to obtain a mixed solvent. In addition,phthalic anhydride (PAH) was dissolved in this mixed solvent finally upto 0.45 mass % as an electrolyte solution. Furthermore, adiponitrile wasdissolved in this mixed solvent finally up to 0.2 mass % as anelectrolyte solution. In this case, the temperature of the mixed liquidwas 29° C. Then, LiPF₆ of 0.6 mol, lithium bis (fluorosulfonyl) imide(LiN(SO₂F)₂) of 0.6 mol, and LiPO₂F₂ of 50 ppm were added per 1 L of themixed solvent, so that an electrolyte solution of Example 130 wasobtained. In this case, the temperature of the electrolyte solution was41° C., and the electrolyte solution was produced by receiving only thethermal history of 50° C. or lower. For the obtained electrolytesolution, it was visually inspected that all of the lithium salts aredissolved.

Comparative Example 116

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:17:3” to obtain a mixed solvent. In thiscase, the temperature of the mixed solvent was 30° C. Then, succinicanhydride (SAH) of 0.02 mass % and LiPF₆ of 1.3 mol were added, and1-methyl-1H-benzotriazole (MBTA) of 0.02 mass % was dissolved, so as toobtain an electrolyte solution of Comparative Example 116. In this case,the temperature of the electrolyte solution was 63° C., and theelectrolyte solution was produced by receiving a thermal history of 50°C. or higher. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved.

Comparative Example 117

Acetonitrile (AcN), diethyl carbonate (DEC), and vinylene carbonate (VC)were mixed under an inert atmosphere at a volume ratio of “41:48:11” toobtain a mixed solvent. Furthermore, adiponitrile was dissolved in thismixed solvent finally up to 3 mass % as an electrolyte solution. In thiscase, the temperature of the mixed solvent was 30° C. Moreover, LiPF₆ of2.0 mol was added, so that an electrolyte solution of ComparativeExample 117 was obtained. In this case, the temperature of theelectrolyte solution was 68° C., and the electrolyte solution wasproduced by receiving a thermal history of 50° C. or higher. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved.

Compositions of each non-aqueous electrolyte solution of Examples 127 to130 and Comparative Examples 116 and 117 are shown in Table 36. Notethat, in Table 36, “AcN” denotes acetonitrile, “DEC” denotes diethylcarbonate, “EMC” denotes ethyl methyl carbonate, “DMC” denotes dimethylcarbonate, “EC” denotes ethylene carbonate, “VC” denotes vinylenecarbonate, “LiPF₆” denotes lithium hexafluorophosphate, “LiN(SO₂F)₂”denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denoteslithium bis (trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole. Preparation was performed such that eachcomponent other than the lithium salt and the additives is a non-aqueoussolvent, and a total amount of each non-aqueous solvent becomes “1 L”.The content of lithium salt is a molar quantity with respect to thenon-aqueous solvent of 1 L.

TABLE 36 Lithium salt Additive Solvent Imide salt Nitrogen- Cyclic AcNDEC EMC DMC EC VC LiPF₆ Content containing acid (vol (vol (vol (vol (vol(vol (mol/1 L (mol/1 L compound anhydride LiPO₂F₂ Thermal %) %) %) %) %)%) solvent) Type solvent) (mass %) (mass %) (ppm) history Example 127 450 36 0 16 3 0.5 LiN(SO₂F)₂ 1.0 — SAH 0.18 3000 ≤50° C. Example 128 55 025 0 16 4 0.3 LiN(SO₂F)₂ 0.7 MBTA 0.3 SAH 0.12 3000 ≤50° C. Example 12931 0 45 0 21 3 0.5 LiN(SO₂F)₂ 0.6 — MAH 0.1 5000 ≤50° C. Example 130 650 0 10 22 3 0.6 LiN(SO₂F)₂ 0.6 Adiponitrile 0.2 PAH 0.45  50 ≤50° C.Comparative 45 0 35 0 17 3 1.3 — — MBTA 0.02 SAH 0.02 — >60° C. Example116 Comparative 41 48 0 0 0 11 2.0 — — Adiponitrile 3.0 — — >60° C.Example 117 Negative- Negative Positive electrode electrodePositive-electrode active electrode active current Battery type materialcurrent collector material collector Separator Example 127 Layeredlaminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copperfoil Polyethylene microporous membrane Example 128 Layered laminate cellLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 129 Layered laminate cellLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 130 Layered laminate cellLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Layered laminate cellLiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene Example 116 microporous membrane Comparative Layeredlaminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foil Graphite Copperfoil Polyethylene Example 117 microporous membrane

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture. N-methyl-2-pyrrolidone as a solvent wasadded to the obtained positive electrode mixture until a solid contentof 68 mass %, and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 11.5 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density: 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 6.9 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.30 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply also referred toas “multi-layered laminate-type battery”) was manufactured.

This multi-layered laminate-type battery has a design capacity value ofapproximately 10 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,a battery was manufactured using the method described in the chapters(1-1) to (1-3), and evaluation was performed in the sequence describedabove in the chapters (2-1) and (2-2). Finally, the ionic conductivitiesat each temperature were calculated in the sequence described in thechapter (2-3).

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. In the following description, “1 C” refers to acurrent value at which the discharge operation is expected to beterminated in one hour by discharging the battery from a full-chargestate of 4.2 V to a voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-Type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the multi-layered laminate-type battery ambient temperatureto 25° C. and was then charged with a constant voltage of 4.2 V for onehour. Then, the battery was discharged with a constant current of 0.2 Cto a voltage of 2.7 V. Then, a sealing portion of the battery wasopened, and degassing was performed inside a glove box having a dewpoint controlled to −60° C. or lower. After the degassing, vacuumsealing was performed under the same environment.

(2-2) 85° C. Full-Charge Storage Test for Multi-Layered Laminate-TypeBattery

For the battery subjected to the initial charging/discharging treatmentas described above in the chapter (2-1), the battery was charged with aconstant current of “1 C” to a voltage of 4.2 V by setting the batteryambient temperature to 25° C., and the battery was then charged with aconstant voltage of 4.2 V for a total of 3 hours. Then, this non-aqueoussecondary battery was stored in a thermostatic oven for 4 hours at 85°C. Then, the battery ambient temperature was recovered to 25° C.

(2-3) Ionic Conductivity Measurement

The electrolyte solution was put into a sealed cell (cell size: 24 mmdiameter, by 0.35 mm thickness) produced by TOYO Corporation, wassealed, and was inserted into a holder (SH1-Z), and wiring wasperformed. In addition, the cell was put into the thermostatic oven, andthe measurement of electrochemical impedance spectroscopy was performed.Gold was used in the electrode. An argon glove box was used until theelectrolyte solution is collected, is filled to the sealed cell, and issealed.

The measurement of electrochemical impedance spectroscopy was performedusing FRA1255 produced by AMETEK Inc. Measurement was performed at anamplitude voltage of 5 mV and a frequency of 10 kHz to 1 MHz. Thetemperature of the thermostatic oven was set to 20° C. and 0° C., andthe measurement was initiated after 1.5 hours from the temperaturesetting. As the measurement data, data at the time point that a changeof the data measured repeatedly at every 5 minutes is lower than 0.1%was employed.

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

As the ionic conductivity, an initial ionic conductivity of theelectrolyte solution and an ionic conductivity of the electrolytesolution collected in the glove box having a dew point controlled to−60° C. or lower after the 85° C. storage test were obtained at 20° C.and 0° C., respectively. The experimental results thereof are shown inTable 37.

TABLE 37 Ion conductivity —N═, Initial ion after 85° C. —NO₄, —N═O,conductivity storage test C—N—N—C, —(NO₃) [mS/cm] [mS/cm] [atomic %] 20°C. 0° C. 20° C. 0° C. Example 127 5.2 21.1 15.8 20.6 14.9 Example 12811.9 20.1 15.3 19.6 14.8 Example 129 4.5 19.0 14.4 17.9 13.9 Example 13010.4 20.9 14.9 19.4 14.3 Comparative 0.2 19.2 15.3 18.0 9.4 Example 116Comparative 25.1 16.9 14.2 15.8 9.2 Example 117

As shown in Table 37, in the examples, it was recognized that the 0° C.ionic conductivity after the storage test for 4 hours at 85° C. is 10mS/cm or higher.

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the positive electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKα 15 kV×3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. Note that a series of operations for sample fabricationwas carried out in an argon glove box (a dew point of −60° C. or lower).The sample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each peak (C1S,O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and a relativesensitivity coefficient of the device. Here, peak splitting wasperformed on the Nis spectrum observed at approximately 394 to 408 eV toderive the area intensity, so that an N-concentration was obtained. Inaddition, within the aforementioned peak range, the peaks observed atapproximately 399 eV to 402 eV have —NH₄, —NH—NH—, (NO₃)—, and N═Obonds.

It was recognized that a decomposition product of thenitrogen-containing compound is suppressed by defining a mixing sequenceof the non-aqueous electrolyte solution, and the non-aqueous electrolytesolution effectively functions as a protection film formation agent ofthe positive electrode.

On the basis of the examples and the comparative examples, it ispreferable that the non-aqueous secondary battery is manufactured usingthe electrolyte solution containing acetonitrile and anitrogen-containing compound. As a result, since a protection film isformed on the positive electrode, it is possible to suppress generationof HF that may cause an increase of the internal resistance.

On the basis of Examples 127 to 130, it was preferable that atemperature increase at the time of adding the nitrogen-containingcompound is suppressed to 50° C. or lower. As a result, it is possibleto suppress thermal decomposition of the nitrogen-containing compoundgenerated at 60° C. or higher.

An example of the thirty ninth embodiment will now be described.

Example 131

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “47:35:16:2” to obtain a mixed solvent. Inaddition, maleic anhydride (MAH) was dissolved in this mixed solventfinally up to 0.10 mass % as an electrolyte solution. Then, LiPF₆ of 0.3mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 1.3 mol, andLiPO₂F₂ of 5000 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 131 was obtained. In this case, theelectrolyte solution was produced by receiving only a thermal history of50° C. or lower. For the obtained electrolyte solution, it was visuallyinspected that all of the lithium salts are dissolved.

Example 132

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:36:16:3” to obtain a mixed solvent. Inaddition, succinic anhydride (SAH) was dissolved in this mixed solventfinally up to 0.30 mass % as an electrolyte solution. Then, LiPF₆ of 0.5mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.8 mol, andLiPO₂F₂ of 2000 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 132 was obtained. In this case, thetemperature of the electrolyte solution is 43° C., and the electrolytesolution was produced by receiving only the thermal history of 50° C. orlower. For the obtained electrolyte solution, it was visually inspectedthat all of the lithium salts are dissolved.

Example 133

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “36:40:20:4” to obtain a mixed solvent. Inaddition, maleic anhydride (MAH) was dissolved in this mixed solventfinally up to 0.2 mass % as an electrolyte solution. Then, LiPF₆ of 0.3mol, lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.6 mol, andLiPO₂F₂ of 2000 ppm were added per 1 L of the mixed solvent, and1-methyl-1H-benzotriazole (MBTA) of 0.35 mass % were dissolved, so thatan electrolyte solution of Example 133 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved.

Example 134

Acetonitrile (AcN), dimethyl carbonate (DMC), ethylene carbonate (EC),and vinylene carbonate (VC) were mixed under an inert atmosphere at avolume ratio of “63:10:22:5” to obtain a mixed solvent. In addition,phthalic anhydride (PAH) was dissolved in this mixed solvent finally upto 0.5 mass % as an electrolyte solution. Then, LiPF₆ of 0.6 mol,lithium bis (fluorosulfonyl) imide (LiN(SO₂F)₂) of 0.6 mol, and LiPO₂F₂of 100 ppm were added per 1 L of the mixed solvent, so that anelectrolyte solution of Example 134 was obtained. In this case, theelectrolyte solution was produced by receiving only the thermal historyof 50° C. or lower. For the obtained electrolyte solution, it wasvisually inspected that all of the lithium salts are dissolved.

Comparative Example 118

Acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate(EC), and vinylene carbonate (VC) were mixed under an inert atmosphereat a volume ratio of “45:35:16:4” to obtain a mixed solvent. In thiscase, the temperature of the mixed solvent was 30° C. Then, phthalicanhydride (PAH) of 2.5 mass % was dissolved. Furthermore, LiPF₆ of 1.3mol was added per 1 L of the mixed solvent, so that an electrolytesolution of Example 118 was obtained. In this case, the temperature ofthe electrolyte solution was 63° C., and the electrolyte solution wasproduced by receiving a thermal history of 50° C. or higher. For theobtained electrolyte solution, it was visually inspected that all of thelithium salts are dissolved.

Comparative Example 119

Acetonitrile (AcN), diethyl carbonate (DEC), and vinylene carbonate (VC)were mixed under an inert atmosphere at a volume ratio of “47:42:11” toobtain a mixed solvent. In this case, the temperature of the mixedsolvent was 30° C. Then, maleic anhydride (MAH) of 2.0 mass % wasdissolved. Furthermore, LiPF₆ of 2.0 mol was added per 1 L of this mixedsolvent, so that an electrolyte solution of Comparative Example 119 wasobtained. In this case, the temperature of the electrolyte solution was63° C., and the electrolyte solution was produced by receiving a thermalhistory of 50° C. or higher. For the obtained electrolyte solution, itwas visually inspected that all of the lithium salts are dissolved.

Compositions of each non-aqueous electrolyte solution of Examples 131 to134 and Comparative Examples 118 and 119 are shown in Table 38. Notethat, in Table 38, “AcN” denotes acetonitrile, “DEC” denotes diethylcarbonate, “EMC” denotes ethyl methyl carbonate, “DMC” denotes dimethylcarbonate, “EC” denotes ethylene carbonate, “VC” denotes vinylenecarbonate, “LiPF₆” denotes lithium hexafluorophosphate, “LiN(SO₂F)₂”denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denoteslithium bis (trifluoromethane sulfonyl) imide, “LiPO₂F₂” denotes lithiumdifluorophosphate, “SAH” denotes succinic anhydride, “MAH” denotesmaleic anhydride, “PAH” denotes phthalic anhydride, and “MBTA” denotes1-methyl-1H-benzotriazole.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 38 Lithium salt Additive Solvent Imide salt Nitrogen- AcN DEC EMCDMC EC LiPF₆ Content containing Cyclic acid (vol (vol (vol (vol (vol VC(mol/1 L (mol/1 L compound anhydride LiPO₂F₂ Thermal %) %) %) %) %) (vol%) solvent) Type solvent) (mass %) (mass %) (ppm) history Example 131 470 35 0 16 2 0.3 LiN(SO₂F)₂ 1.3 — MAH 0.10 5000 ≤50° C. Example 132 45 036 0 16 3 0.5 LiN(SO₂F)₂ 0.8 — SAH 0.30 2000 ≤50° C. Example 133 36 0 400 20 4 0.3 LiN(SO₂F)₂ 0.6 MBTA 0.35 MAH 0.2 2000 ≤50° C. Example 134 630 0 10 22 5 0.6 LiN(SO₂F)₂ 0.6 — PAH 0.5  100 ≤50° C. Comparative 45 035 0 16 4 1.3 — — — PAH 2.5 — >60° C. Example 118 Comparative 47 42 0 00 11 2.0 — — — MAH 2.0 — >60° C. Example 119 Positive Negative- Negativeelectrode electrode electrode Positive-electrode active current activecurrent Battery type material collector material collector SeparatorExample 131 Layered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminumfoil Graphite Copper foil Polyethylene microporous membrane Example 132Layered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane Example 133Layered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane Example 134Layered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane ComparativeLayered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene Example 118 microporous membraneComparative Layered laminate cell LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂ Aluminumfoil Graphite Copper foil Polyethylene Example 119 microporous membrane

<Manufacturing of Non-Aqueous Secondary Battery>

(1-1) Fabrication of Positive Electrode

A composite oxide of lithium having a number average particle diameterof 11 μm, nickel, manganese and cobalt (Ni/Mn/Co=1/1/1 (element ratio),density: 4.70 g/cm³) as the positive-electrode active material, graphitecarbon powder (density: 2.26 g/cm³) having a number average particlediameter of 6.5 μm and acetylene black powder (density: 1.95 g/cm³)having a number average particle diameter of 48 nm as the conductiveaid, and polyvinylidene fluoride (PVdF, density: 1.75 g/cm³) as thebinder were mixed at a mass ratio of “100:4.2:1.8:4.6” to obtain apositive electrode mixture. N-methyl-2-pyrrolidone as a solvent wasadded to the obtained positive electrode mixture until a solid contentof 68 mass %, and they were further mixed to prepare positive electrodemixture-containing slurry. This positive electrode mixture-containingslurry was coated on both surfaces of an aluminum foil having athickness of 20 μm and a width of 200 mm, which will serve as a positiveelectrode current collector, using a doctor blade method while adjustingthe basis weight of one surface to 11.5 mg/cm², and the solvent wasdried and removed. When the positive electrode mixture-containing slurrywas coated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine to an actual electrode density of 2.80 g/cm³,and a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the coated portion hasan area of 150 mm by 150 mm. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 h at 120° C.,so that a lead-attached positive electrode was obtained.

(1-2) Fabrication of Negative Electrode

Graphite carbon powder (density: 2.23 g/cm³) having a number averageparticle diameter of 12.7 μm and graphite carbon powder (density 2.27g/cm³) having a number average particle diameter of 6.5 μm as thenegative-electrode active material, a carboxymethyl cellulose (density:1.60 g/cm³) solution (solid content concentration: 1.83 mass %) as thebinder, and diene-based rubber (glass transition temperature: −5° C.,number average particle diameter when dried: 120 nm, density: 1.00g/cm³, dispersion medium: water, solid content concentration: 40 mass %)were mixed at a solid content mass ratio of “87.2:9.7:1.4:1.7” to obtaina negative electrode mixture. Water as a solvent was added to theobtained negative electrode mixture until a solid content of 45 mass %,and they were further mixed to prepare negative electrodemixture-containing slurry. This negative electrode mixture-containingslurry was coated on both surfaces of a copper foil having a thicknessof 10 μm and a width of 200 mm, which will serve as a negative electrodecurrent collector, using a doctor blade method while adjusting the basisweight of one surface to 6.9 mg/cm², and the solvent was dried andremoved. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine to an actual electrode density of 1.30 g/cm³, and anegative electrode having the negative-electrode active material layerand the negative electrode current collector was obtained.

Then, this negative electrode was cut such that the coated portion hasan area of 152 mm by 152 mm. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 h at 80° C., so that alead-attached negative electrode was obtained.

(1-3) Fabrication of Layered Laminate Non-Aqueous Secondary Battery

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene resin film whilethe mixture coat surfaces of each electrode face each other, so that alaminated electrode structure was obtained. This laminated electrodestructure was housed in an aluminum laminated sheet package, and vacuumdrying was performed for 5 h at 80° C. in order to remove moisture.Subsequently, an electrolyte solution was injected into the package, andthe package was sealed, so that a layered laminate non-aqueous secondarybattery (pouch type cell battery, hereinafter, simply referred to as“multi-layered laminate-type battery”) was manufactured.

This multi-layered laminate-type battery has a design capacity value ofapproximately 10 Ah and a rated voltage value of 4.2 V.

<Evaluation of Multi-Layered Laminate-Type Battery>

For the multi-layered laminate-type battery obtained as described above,initial charging/discharging treatment was performed in the sequencedescribed in the chapter (2-1). Subsequently, the battery was evaluatedin the sequence of the chapters (2-2) and (2-3). Furthermore, theelectrolyte solution was evaluated in the sequence of the chapter (2-4).

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. In the following description, “1 C” refers to acurrent value at which the discharge operation is expected to beterminated in one hour by discharging the battery from a full-chargestate of 4.2 V to a voltage of 2.7 V at a constant current.

(2-1) Initial Charging/Discharging Treatment of Multi-LayeredLaminate-Type Battery

As a charging device, a battery tester PFX2011 produced by KikusuiElectronics Co., Ltd. was employed. The multi-layered laminate-typebattery was charged with a constant current of 0.2 C to a voltage of 4.2V by setting the ambient temperature to 25° C. and was then charged witha constant voltage of 4.2 V for one hour. Then, the battery wasdischarged with a constant current of 0.2 C to a voltage of 2.7 V. Then,a sealing portion of the battery was opened, and degassing was performedinside a glove box having a dew point controlled to −60° C. or lower.After the degassing, vacuum sealing was performed under the sameenvironment.

(2-2) 85° C. Full-Charge Storage Test for Multi-Layered Laminate-TypeBattery

For the battery subjected to the initial charging/discharging treatmentas described above in the chapter (2-1), the battery was charged with aconstant current of “1 C” to a voltage of 4.2 V by setting the batteryambient temperature to 25° C., and the battery was then charged with aconstant voltage of 4.2 V for a total of 3 hours. Then, this non-aqueoussecondary battery was stored in a thermostatic oven for 4 hours at 85°C. Then, the battery ambient temperature was recovered to 25° C.

(2-3) Ionic Conductivity Measurement

The electrolyte solution was put into a sealed cell (cell size: 24 mmdiameter by 0.35 mm thickness) produced by TOYO Corporation, was sealed,and was inserted into a holder (SH1-Z), and wiring was performed.

In addition, the cell was put into the thermostatic oven, and themeasurement of electrochemical impedance spectroscopy was performed.Gold was used in the electrode. An argon glove box was used until theelectrolyte solution is collected, is filled to the sealed cell, and issealed.

The obtained data was plotted on a Nyquist diagram including real partsZ′ and imaginary parts Z″ of impedance. In addition, a Z′ value (R) atZ″=0 was read, and the Li ionic conductivity was obtained using thefollowing formula.Li ionic conductivity (mS/cm)=d/(R·S)

Here, “d” denotes a distance between electrodes (0.35 cm), and “S”denotes an area of the electrode (4.522 cm²).

As the ionic conductivity, an initial ionic conductivity of theelectrolyte solution and an ionic conductivity of the electrolytesolution collected in the glove box having a dew point controlled to−60° C. or lower after the 85° C. storage test were obtained at 20° C.and 0° C., respectively. The experimental results thereof are shown inTable 39.

TABLE 39 Ion Organic conductivity acid or Initial ion after 85° C. saltthereof, conductivity storage test LiO₂ [mS/cm] [mS/cm] [atomic %] 20°C. 0° C. 20° C. 0° C. Example 131 11.5 21.6 16.5 20.5 15.0 Example 13217.2 20.5 15.7 18.3 14.6 Example 133 15.4 18.6 13.7 18.0 13.1 Example134 18.9 21.0 15.2 20.1 14.2 Comparative 38.1 18.5 14.7 17.3 8.7 Example118 Comparative 39.6 16.8 13.9 14.6 8.1 Example 119

As shown in Table 39, in the examples, it was recognized that the 0° C.ionic conductivity after the storage test for 4 hours at 85° C. is 10mS/cm or higher.

In this example, an X-ray photoelectron spectroscopy (XPS) analysis wasperformed for a surface portion of the negative electrode in thebattery. As an XPS analyzer, Versa Probell produced by ULVAC-PHI, Inc.was employed. As an analysis condition, an excitation source was set tomono. AlKα 15 kV×3.3 mA, an analysis size was set to approximately 200μm diameter, and a photoelectron emission angle was set to 45°±20°. Inaddition, the measurement sample was disassembled from the batterybefore the test, and the obtained electrode was immersed in acetonitrilefor approximately one minute to wash the electrolyte solution adheringto the sample. Then, the sample was air-dried for 12 hours. The driedsample was cut into small pieces of 3 mm square and was used as an XPSanalysis sample. A series of operations for sample fabrication wascarried out in an argon glove box (a dew point of −60° C. or lower). Thesample was delivered to the XPS device without exposure to theatmosphere using a dedicated tool. A relative element concentration ofeach element was obtained using the area intensity of each peak (C1S,O1s, F1s, P2p, N1s, S2p, Li1s, Mn3p, Ni3p, and Co3p) and a relativesensitivity coefficient of the device. Here, peak splitting wasperformed on the O1s spectrum observed at approximately 524 to 540 eV toderive the area intensity, so that an O-concentration was obtained. Inaddition, within the aforementioned peak range, the peaks observed atapproximately 528 eV have Li₂O, and the peaks observed at approximately530 to 535 eV have an organic product or salt thereof. The “atomic %” ofTable 39 refers to an oxygen concentration in atomic % when peaksplitting of the photoelectron spectrum is performed.

It was recognized that a decomposition product of the LiPF₆ issuppressed and resistance of the thermal history can be obtained bydefining a mixing sequence of the non-aqueous electrolyte solution.

On the basis of the examples and the comparative examples, it ispreferable that the non-aqueous secondary battery is manufactured usingthe electrolyte solution obtained by adding acetonitrile and cyclic acidanhydride and then adding LiPF₆. As a result, it is possible to suppressan abrupt temperature increase at the timing of adding LiPF₆, andsuppress generation of HF that may cause an increase of the internalresistance due to a sacrificial response of the cyclic acid anhydride.

On the basis of Examples 131 to 134, it was preferable that atemperature increase at the time of adding LiPF₆ is suppressed to 50° C.or lower. As a result, it is possible to suppress thermal decompositionof LiPF₆ generated at 60° C. or higher.

An example of the fortieth embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 40. Note that, in Table 40, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “MBTA” denotes1-methyl-1H-benzotriazole, “SAH” denotes succinic anhydride, and“LiPO₂F₂” denotes lithium difluorophosphate.

Preparation was performed such that each component other than thelithium salt and the additives is a non-aqueous solvent, and a totalamount of each non-aqueous solvent becomes “1 L”. The content of lithiumsalt is a molar quantity with respect to the non-aqueous solvent of 1 L.

A non-aqueous secondary battery using the positive-electrode activematerial, the negative-electrode active material, and electrolytesolution of Table 40 was manufactured.

TABLE 40 Lithium salt Additive Imide salt Nitrogen- Cyclic Solvent LiPF₆Content containing acid AcN DEC EMC DMC EC VC (mol/1 L (mol/1 L compoundanhydride LiPO₂F₂ (vol %) (vol %) (vol %) (vol %) (vol %) (vol %)solvent) Type solvent) (mass %) (mass %) (ppm) Example 135 51 24 0 0 214 0.5 LiN(SO₂F)₂ 0.6 MBTA 0.2 SAH 0.1 2000 Example 136 25 23 28 0 21 30.3 LiN(SO₂F)₂ 1.0 MBTA 0.4 SAH 0.2 5000 Example 137 60 0 0 18 18 4 0.5LiN(SO₂CF₃)₂ 0.7 MBTA 0.2 SAH 0.1 2000 Comparative 0 47 16 0 34 3 1.2 —— — — — Example 120 Comparative 0 0 20 45 33 2 0.3 LiN(SO₂F)₂ 0.9 — — —Example 121 Negative- negative Positive electrode electrodePositive-electrode electrode active current Battery type active materialcurrent collector material collector separator Example 135Single-layered laminate LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ Aluminum foil Blacklead Copper foil Polyethylene microporous membrane Example 136Single-layered laminate LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ Aluminum foil Blacklead Copper foil Polyethylene microporous membrane Example 137Single-layered laminate LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ Aluminum foil Blacklead Copper foil Polyethylene microporous membrane ComparativeSingle-layered laminate LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂ Aluminum foil Blacklead Copper foil Polyethylene microporous Example 120 membraneComparative Single-layered laminate LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂Aluminum foil Black lead Copper foil Polyethylene microporous Example121 membrane

<Fabrication of Positive Electrode>

A composite oxide (LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂) of lithium, nickel,manganese, and cobalt as the positive-electrode active material,acetylene black powder as the conductive aid, and polyvinylidenefluoride (PVDF) as the binder were mixed at a mass ratio of“100:4.3:4.3” to obtain a positive electrode mixture.N-methyl-2-pyrrolidone as a solvent was added to the obtained positiveelectrode mixture, and they were further mixed to prepare positiveelectrode mixture-containing slurry. This positive electrodemixture-containing slurry was coated on one surface of an aluminum foilhaving a thickness of 15 μm, which will serve as a positive electrodecurrent collector, while adjusting the basis weight to 180 g/m². Whenthe positive electrode mixture-containing slurry was coated on thealuminum foil, an uncoated region was formed so as to expose a part ofthe aluminum foil. Then, roll pressing was performed using a roll pressmachine until the positive-electrode active material layer has a densityof 2.80 mg/cm³, so that a positive electrode having thepositive-electrode active material layer and the positive electrodecurrent collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 14 mm by 20 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, acetylene blackpowder as the conductive aid, polyvinylidene fluoride (PVDF) as thebinder were mixed at a mass ratio of “100:2.2:5.4” to obtain a negativeelectrode mixture. N-methyl-2-pyrrolidone as a solvent was added to theobtained negative electrode mixture, and they were further mixed toprepare negative electrode mixture-containing slurry. This slurry wascoated on one surface of a copper foil having a thickness of 10 μm to aconstant thickness while adjusting the basis weight to approximately110.0 g/m². When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine until the negative-electrode active material layerhas a density of 1.5 g/cm³, so that a negative electrode having thenegative-electrode active material layer and the negative electrodecurrent collector was obtained.

Then, this negative electrode was cut such that the negative electrodemixture layer has an area of 15 mm by 21 mm, and the exposed portion ofthe copper foil is included. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 hours at 80° C., so that alead-attached negative electrode was obtained.

<Assembly of Single-Layered Laminate-Type Battery>

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene microporousmembrane separator (having a thickness of 21 μm) while the mixture coatsurfaces of each electrode face each other, so that a laminatedelectrode structure was obtained. This laminated electrode structure washoused in an aluminum laminated sheet package having a size of 90 mm by80 mm, and vacuum drying was performed for 5 hours at 80° C. in order toremove moisture. Subsequently, each of the electrolyte solutionsdescribed above was injected into the package, and the package wassealed, so that a single-layered laminate type (pouch type) non-aqueoussecondary battery (hereinafter, simply referred to as “single-layeredlaminate-type battery”) was manufactured. This single-layeredlaminate-type battery has a design capacity value of 7.5 mAh and a ratedvoltage value of 4.2 V.

<Evaluation of Single-Layered Laminate-Type Battery>

Each battery for evaluation obtained as described above was evaluated inthe following sequence.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 2.5 V at a constant current.

<4.2V Cycle Test for Single-Layered Laminate-Type Battery>

The battery was charged to a voltage 4.2 V with a constant current of7.5 mA corresponding to “1 C” by setting the battery ambient temperatureto 25° C., and was then discharged with a constant current of 7.5 mA toa voltage of 2.7 V. By setting one charge operation and one dischargeoperation as a single cycle, the charging/discharging was performed for100 cycles. The discharge capacity of the hundredth cycle was set as acapacity retention rate by assuming that the discharge capacity of thefirst cycle is 100%.

<4.3V Cycle Test for Single-Layered Laminate-Type Battery>

The battery was charged to a voltage 4.3 V with a constant current of7.5 mA corresponding to “1 C” by setting the battery ambient temperatureto 25° C., and was then discharged to a voltage of 2.7 V with a constantcurrent of 7.5 mA. By setting one charge operation and one dischargeoperation as a single cycle, the charging/discharging was performed for100 cycles. The discharge capacity of the hundredth cycle was set as acapacity retention rate by assuming that the discharge capacity of thefirst cycle is 100%. The experimental results thereof are shown in Table41.

TABLE 41 Capacity retention Capacity retention rate in 4.2 V cycle ratein 4.3 V cycle test test Example 135 99% 94% Example 136 99% 94% Example137 98% 93% Comparative Example 120 38% 55% Comparative Example 121 39%57%

In the examples, it was recognized that the capacity retention rate ofthe hundredth cycle is 90% or higher, and a high capacity retention rateis maintained.

On the basis of the experimental results of these examples andcomparative examples, it was preferable that the non-aqueous secondarybattery includes a positive electrode having a positive-electrode activematerial layer formed on one or both sides of a current collector, anegative electrode having a negative-electrode active material layerformed on one or both sides of a current collector, and a non-aqueouselectrolyte solution containing acetonitrile and lithium salt. As aresult, since the electrolyte solution containing acetonitrile and anitrogen-containing compound is employed, an increase of the internalresistance caused by the electrolyte solution is negligible even when ahigh-voltage charging/discharging cycle is performed. In particular, itis possible to suppress an increase of the interface resistance.

On the basis of these examples and comparative examples, it waspreferable that the content of the nickel element in thepositive-electrode active material is more than 50%. Using theelectrolyte solution containing acetonitrile and the nitrogen-containingcompound, it is possible to suppress capacity degradation caused by anunstable crystal structure even when the nickel content increases.

On the basis of Examples 135 to 137, in the non-aqueous secondarybattery obtained by using the high nickel positive electrode as thepositive-electrode active material, it was preferable that the chargingvoltage is set to 4.3 V or higher. As a result, it is possible to setthe design capacity to 150 Ah/L or larger.

Next, an example of the forty first embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 42. Note that, in Table 42, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “MBTA” denotes1-methyl-1H-benzotriazole, “LiPO₂F₂” denotes lithium difluorophosphate,“SAH” denotes succinic anhydride, “MAH” denotes maleic anhydride, “PAH”denotes phthalic anhydride, and “LiPO₂F₂” denotes lithiumdifluorophosphate.

Preparation was performed such that each component other than lithiumsalts and additives is a non-aqueous solvent, and a total amount of eachnon-aqueous solvent becomes “1 L”.

TABLE 42 Lithium salt Additive Imide salt Nitrogen- Cyclic Solvent LiPF₆Content containing acid AcN DEC EMC DMC EC VC (mol/1 L (mol/1 L compoundanhydride LiPO₂F₂ (vol %) (vol %) (vol %) (vol %) (vol %) (vol %)solvent) Type solvent) (mass %) (mass %) (ppm) Example 138 45 30 0 0 214 0.7 LiN(SO₂CF₃)₂ 0.3 — MAH 0.2 8000 Example 139 47 28 0 0 21 4 0.3LiN(SO₂F)₂ 1.0 — PAH 0.6 100 Example 140 65 0 0 13 18 4 0.6 LiN(SO2CF3)₂0.6 MBTA 0.2 SAH 0.6 100 Example 141 47 0 30 0 20 3 0.6 LiN(SO₂F)₂ 0.6MBTA 0.2 MAH 0.8 5000 Comparative 0 72 0 0 24 4 1.2 — — — — — Example122 Comparative 0 0 66 0 32 2 1.0 LiN(SO₂CF₃)₂ 0.6 MBTA 0.2 SAH 1.5 —Example 123 Comparative 0 25 0 48 25 2 0.7 LiN(SO₂F)₂ 0.5 — — — Example124 Negative- Negative electrode electrode Positive-electrode activePositive electrode active current Battery type material currentcollector material collector Separator Example 138 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 139 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 140 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 141 Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Layered laminate cellLiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copper foilPolyethylene Example 122 microporous membrane Comparative Layeredlaminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copperfoil Polyethylene Example 123 microporous membrane Comparative Layeredlaminate cell LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂ Aluminum foil Graphite Copperfoil Polyethylene Example 124 microporous membrane

<Manufacturing of Battery>

<Fabrication of Positive Electrode>

A composite oxide (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂) or(LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂) of lithium, nickel, manganese, and cobaltas the positive-electrode active material, acetylene black powder as theconductive aid, and polyvinylidene fluoride (PVDF) as the binder weremixed at a mass ratio of “100:3.5:3” to obtain a positive electrodemixture. N-methyl-2-pyrrolidone as a solvent was added to the obtainedpositive electrode mixture, and they were further mixed to preparepositive electrode mixture-containing slurry. This positive electrodemixture-containing slurry was coated on one surface of an aluminum foilhaving a thickness of 15 μm, which will serve as a positive electrodecurrent collector, while adjusting the basis weight to approximately95.0 g/m². When the positive electrode mixture-containing slurry wascoated on the aluminum foil, an uncoated region was formed so as toexpose a part of the aluminum foil. Then, roll pressing was performedusing a roll press machine until the positive-electrode active materiallayer has a density of 2.50 g/cm³, so that a positive electrode havingthe positive-electrode active material layer and the positive electrodecurrent collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 30 mm by 50 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, carboxymethylcellulose as the binder, and styrene-butadiene latex as the binder weremixed at a mass ratio of “100:1.1:1.5” to obtain a negative electrodemixture. An appropriate amount of water was added to the obtainednegative electrode mixture, and they were mixed sufficiently to preparenegative electrode mixture-containing slurry. This slurry was coated onone surface of a copper foil having a thickness of 10 μm to a constantthickness. When the negative electrode mixture-containing slurry wascoated on the copper foil, an uncoated region was formed so as to exposea part of the copper foil. Then, roll pressing was performed using aroll press machine until the negative-electrode active material layerhas a density of 1.35 g/cm³, so that a negative electrode having thenegative-electrode active material layer and the negative electrodecurrent collector was obtained.

In the experiment, a battery voltage was measured after one hour fromthe injection. The experimental result is shown in the following Table43.

TABLE 43 Negative Positive electrode electrode Battery potentialpotential voltage [V vs. Li/Li⁺] [V vs. Li/Li+] [V] Example 138 3.2 2.580.62 Example 139 3.2 2.57 0.63 Example 140 3.2 2.57 0.63 Example 141 3.22.61 0.59 Comparative Example 122 3.2 3.13 0.07 Comparative Example 1233.2 3.12 0.08 Comparative Example 124 3.2 3.12 0.08

As shown in Table 43, in all of the examples, a difference of thenegative electrode electric potential around the injection of thenon-aqueous electrolyte solution was 0.3 V or higher.

On the basis of the experiments, it was preferable that the negativeelectrode contains at least one of metals having a standard electrodepotential of 0 V or higher. Since the negative electrode of thenon-aqueous secondary battery using the existing carbonate electrolytesolution has an electric potential close to 3.1 V vs. Li/Li⁺ afterliquid injection, elution of a metal element having a high standardelectrode potential gradually proceeds as it is stored for a long time.Meanwhile, the electrolyte solution using acetonitrile does not causeelution even when it is stored for a long time after liquid injection.Therefore, it is possible to extend a manufacturing control periodincluding an impregnation time.

On the basis of the experimental results of Examples 138 to 141, thenegative electrode current collector is preferably formed of copper. Asa result, it is possible to suppress elution of copper withoutgenerating a charging/discharging history.

Next, an example of the forty second embodiment will now be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 44. Note that, in Table 44, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “EC” denotes ethylene carbonate, “VC” denotes vinylenecarbonate, “LiPF₆” denotes lithium hexafluorophosphate, “LiN(SO₂F)₂”denotes lithium bis (fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denoteslithium bis (trifluoromethane sulfonyl) imide, “SAH” denotes succinicanhydride, “MAH” denotes maleic anhydride, “PAH” denotes phthalicanhydride, and “LiPO₂F₂” denotes lithium difluorophosphate.

Preparation was performed such that each component other than lithiumsalts and additives is a non-aqueous solvent, and a total amount of eachnon-aqueous solvent becomes “1 L”. The content of lithium salt is amolar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 44 Lithium salt Imide salt Additive Solvent LiPF₆ LiBOB ContentCyclic acid Acetic AcN DEC EMC EC VC (mol/1 L (mol/1 L (mol/1 Lanhydride LiPO₂F₂ acid (vol %) (vol %) (vol %) (vol %) (vol %) solvent)solvent) Type solvent) (mass %) (ppm) (ppm) Example 142 50 35 0 11 4 0.30 LiN(SO₂F)₂ 1.0 SAH 0.2 5000 0.1 Example 143 35 0 40 21 4 0.5 0LiN(SO₂F)₂ 0.7 MAH 0.15 1000 1 Example 144 65 25 0 6 4 0.3 0LiN(SO₂CF₃)₂ 1.2 PAH 0.5 5000 5 Comparative 47 42 0 0 11 1.3 0.2 — — MAH0.01 — — Example 122 Comparative 85 11 0 0 4 1 0 — — — 5 Example 123Positive Negative electrode Negative- electrode Positive-electrodecurrent electrode current Battery type active material collector activematerial collector Separator Example 142 Layered laminateLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 143 Layered laminateLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 144 Layered laminateLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Layered laminateLiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous Example 122 membrane Comparative Layeredlaminate LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous Example 123 membrane

<Manufacturing of Battery>

<Fabrication of Positive Electrode>

A composite oxide (LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂) of lithium, nickel,manganese, and cobalt as the positive-electrode active material,acetylene black powder as the conductive aid, and polyvinylidenefluoride (PVDF) as the binder were mixed at a mass ratio of “100:3.5:3”to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as asolvent was added to the obtained positive electrode mixture, and theywere further mixed to prepare positive electrode mixture-containingslurry. This positive electrode mixture-containing slurry was coated onone surface of an aluminum foil having a thickness of 15 μm, which willserve as a positive electrode current collector, while adjusting thebasis weight to approximately 95.0 g/m². When the positive electrodemixture-containing slurry was coated on the aluminum foil, an uncoatedregion was formed so as to expose a part of the aluminum foil. Then,roll pressing was performed using a roll press machine until thepositive-electrode active material layer has a density of 2.50 g/cm³, sothat a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 30 mm by 50 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, carboxymethylcellulose as the binder, and styrene-butadiene latex as the binder weremixed at a mass ratio of “100:1.1:1.5” to obtain a negative electrodemixture. An appropriate amount of water was added to the obtainednegative electrode mixture, and they were mixed sufficiently to preparenegative electrode mixture-containing slurry. This slurry was coated onone surface of a copper foil having a thickness of 10 μm to a constantthickness while adjusting the basis weight to 60.0 g/m². When thenegative electrode mixture-containing slurry was coated on the copperfoil, an uncoated region was formed so as to expose a part of the copperfoil. Then, roll pressing was performed using a roll press machine untilthe negative-electrode active material layer has a density of 1.35g/cm³, so that a negative electrode having the negative-electrode activematerial layer and the negative electrode current collector wasobtained.

Then, this negative electrode was cut such that the negative electrodemixture layer has an area of 32 mm by 52 mm, and the exposed portion ofthe copper foil is included. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 hours at 80° C., so that alead-attached negative electrode was obtained.

<Assembly of Single-Layered Laminate-type Battery>

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene microporousmembrane separator (having a thickness of 21 μm) while the mixture coatsurfaces of each electrode face each other, so that a laminatedelectrode structure was obtained. This laminated electrode structure washoused in an aluminum laminated sheet package having a size of 90 mm by80 mm, and vacuum drying was performed for 5 hours at 80° C. in order toremove moisture. Subsequently, each of the electrolyte solutionsdescribed above was injected into the package, and the package wassealed, so that a single-layered laminate type (pouch type) non-aqueoussecondary battery (hereinafter, simply referred to as “single-layeredlaminate-type battery”) was manufactured. This single-layeredlaminate-type battery has a design capacity value of 23 mAh and a ratedvoltage value of 4.2 V.

<Evaluation of Single-Layered Laminate-Type Battery>

For the battery for evaluation obtained as described above, first,initial charging treatment was performed in the sequence of thefollowing chapter (1-1). Then, each battery was evaluated in thesequence of the chapter (1-2). Note that the charging/discharging wasperformed using a charging/discharging device ACD-01 (model name)produced by Asuka Electronics Co., Ltd. and a thermostatic oven PLM-63S(model name) produced by Futaba Kagaku Co., Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current.

(1-1) Initial Charging/Discharging Treatment of Single-LayeredLaminate-Type Battery

The battery was charged with a constant current of 2.3 mA correspondingto “0.1 C” to a voltage of 4.2 V by setting the battery ambienttemperature to 25° C. and was then charged with a constant voltage of4.2 V for 1.5 hours. Then, the battery was discharged with a constantcurrent of 6.9 mA corresponding to “0.3 C” to a voltage of 3.0 V.Initial efficiency was calculated by dividing the discharge capacity atthis time by the charge capacity.

(1-2) 60° C. Storage Test for Single-Layered Laminate-Type Battery

In the experiment, the single-layered laminate-type battery was chargedto a voltage of 4.2 V with a constant current of 0.05 C at a temperatureof 25° C., and was then charged with a constant voltage of 4.2 V for 1.5hours. In addition, this charged single-layered laminate-type batterywas stored in a thermostatic oven of 60° C. After 200 hours, thesingle-layered laminate-type battery was removed from the thermostaticoven, and was recovered to the room temperature. Then, the 4.2 V storagecharacteristics of the single-layered laminate-type battery wereevaluated using the technique of measuring a gas generation amount and avoltage of each laminated cell. The gas generation amount was measuredusing the Archimedes method, in which the single-layered laminate-typebattery is put into the container filled with hyper-pure water, and thevolume of the single-layered laminate-type battery is measured from aweight change around that time. As a device for measuring the volumefrom the weight change, a gravimeter MDS-300 produced by Alfa MirageCo., Ltd. was employed.

TABLE 45 Gas generation amount in 60° C. Equivalent value storage testper 1 mAh (ml) (ml) determination Example 142 0.10 0.0043 ∘ Example 1430.12 0.0052 ∘ Example 144 0.13 0.0057 ∘ Comparative 0.47 0.0200 xExample 122 Comparative Evaluation stop Evaluation stop x Example 123

As shown in Table 45, in the examples, it was recognized that the gasgeneration amount in the storage test for 200 hours at 60° C. is 0.008ml or less per 1 mAh. Preferably, the gas generation amount is 0.007 mlor less per 1 mAh.

In this example, the non-aqueous secondary battery containsacetonitrile, LiPO₂F₂, acetic acid, and cyclic acid anhydride. As aresult, LiPO₂F₂, acetic acid, and cyclic acid anhydride function as areduction resistance, and acetonitrile is reductively decomposed, sothat it is possible to suppress generation of gas. In addition, thebattery is preferably a pouch type non-aqueous secondary batterycontaining acetonitrile, LiPO₂F₂, acetic acid, and cyclic acidanhydride. As a result, an SEI is formed on the surface of the negativeelectrode due to LiPO₂F₂, acetic acid, and cyclic acid anhydride, sothat it is possible to suppress promotion of reduction of acetonitrile.

On the basis of Examples 142 to 144, it is preferable that the contentof acetic acid is set to 0.1 ppm or more and 5 ppm or less with respectto the non-aqueous electrolyte solution. The gas generation amount inthe storage test for 200 hours at 60° C. can be more effectively set to0.008 ml or less per 1 mAh.

Next, an example of the forty third embodiment will be described.

<Preparation of Electrolyte Solution>

An electrolyte solution was prepared by mixing various solvents andadditives at a predetermined volume ratio. The compositions of eachelectrolyte solution used in the examples and the comparative examplesare shown in Table 46. Note that, in Table 46, “AcN” denotesacetonitrile, “DEC” denotes diethyl carbonate, “EMC” denotes ethylmethyl carbonate, “DMC” denotes dimethyl carbonate, “EC” denotesethylene carbonate, “VC” denotes vinylene carbonate, “LiPF₆” denoteslithium hexafluorophosphate, “LiN(SO₂F)₂” denotes lithium bis(fluorosulfonyl) imide, “LiN(SO₂CF₃)₂” denotes lithium bis(trifluoromethane sulfonyl) imide, “MBTA” denotes1-methyl-1H-benzotriazole, “SAH” denotes succinic anhydride, “MAH”denotes maleic anhydride, and “PAH” denotes phthalic anhydride, “MBTA”denotes 1-methyl-1H-benzotriazole, and “LiPO₂F₂” denotes lithiumdifluorophosphate.

Preparation was performed such that each component other than lithiumsalt and additives is a non-aqueous solvent, and a total amount of eachnon-aqueous solvent becomes “1 L”. The content of lithium salt is amolar quantity with respect to the non-aqueous solvent of 1 L.

TABLE 46 Lithium salt Additive Imide salt Nitrogen- Cyclic solvent LiPF₆Content containing acid AcN DEC EMC DMC EC VC (mol/1 L (mol/1 L compoundanhydride LiPO₂F₂ (vol %) (vol %) (vol %) (vol %) (vol %) (vol %)solvent) Type solvent) (mass %) (mass %) (ppm) Example 145 45 0 35 0 164 0.3 LiN(SO₂F)₂ 1.0 — MAH 0.2 3000 Example 146 50 35 0 0 10 5 0.5LiN(SO₂F)₂ 0.7 MBTA 0.2 SAH 0.2 8000 Example 147 65 0 0 6 22 7 0.5LiN(SO₂CF₃)₂ 0.6 MBTA 0.1 PAH 0.4 100 Comparative 47 42 0 0 0 11 1.3LiN(SO₂F)₂ 1 — MAH 0.05 — Example 124 Comparative 23 0 42 0 20 15 0.6LiN(SO₂CF₃)₂ 0.6 — — 5 Example 125 Comparative 100 0 0 0 0 0 0LiN(SO₂CF₃)₂ 4.2 — — — Example 126 Negative- Negative electrodeelectrode Positive-electrode Positive electrode active current Batterytype active material current collector material collector SeparatorExample 145 Coin (CR2032) LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foilGraphite Copper foil Polyethylene microporous membrane Example 146 Coin(CR2032) LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Example 147 Coin (CR2032)LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene microporous membrane Comparative Coin (CR2032)LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene Example 124 microporous membrane Comparative Coin (CR2032)LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene Example 125 microporous membrane Comparative Coin (CR2032)LiNi_(1/3)Co_(1/3)Mn_(1/3)O₂ Aluminum foil Graphite Copper foilPolyethylene Example 126 microporous membrane

<Manufacturing of Battery>

<Fabrication of Positive Electrode>

A composite oxide (LiN_(1/3)Mn_(1/3)Co_(1/3)O₂) of lithium, nickel,manganese, and cobalt as the positive-electrode active material,acetylene black powder as the conductive aid, and polyvinylidenefluoride (PVDF) as the binder were mixed at a mass ratio of “100:3.5:3”to obtain a positive electrode mixture. N-methyl-2-pyrrolidone as asolvent was added to the obtained positive electrode mixture, and theywere further mixed to prepare positive electrode mixture-containingslurry. This positive electrode mixture-containing slurry was coated onone surface of an aluminum foil having a thickness of 15 μm, which willserve as a positive electrode current collector, while adjusting thebasis weight to 95.0 g/m². When the positive electrodemixture-containing slurry was coated on the aluminum foil, an uncoatedregion was formed so as to expose a part of the aluminum foil. Then,roll pressing was performed using a roll press machine until thepositive-electrode active material layer has a density of 2.74 g/cm³, sothat a positive electrode having the positive-electrode active materiallayer and the positive electrode current collector was obtained.

Then, this positive electrode was cut such that the positive electrodemixture layer has an area of 30 mm by 50 mm, and an exposed portion ofthe aluminum foil is included. In addition, a lead piece formed ofaluminum for extracting a current was welded to the exposed portion ofthe aluminum foil, and vacuum drying was performed for 12 hours at 120°C., so that a lead-attached positive electrode was obtained.

<Fabrication of Negative Electrode>

Graphite as the negative-electrode active material, carboxymethylcellulose as the binder, and styrene-butadiene latex as the binder weremixed at a mass ratio of “100:1.1:1.5” to obtain a negative electrodemixture. An appropriate amount of water was added to the obtainednegative electrode mixture, and they were mixed sufficiently to preparenegative electrode mixture-containing slurry. This slurry was coated onone surface of a copper foil having a thickness of 10 μm to a constantthickness while adjusting the basis weight to 61.0 g/m². When thenegative electrode mixture-containing slurry was coated on the copperfoil, an uncoated region was formed so as to expose a part of the copperfoil. Then, roll pressing was performed using a roll press machine untilthe negative-electrode active material layer has a density of 1.50g/cm³, so that a negative electrode having the negative-electrode activematerial layer and the negative electrode current collector wasobtained.

Then, this negative electrode was cut such that the negative electrodemixture layer has an area of 32 mm by 52 mm, and the exposed portion ofthe copper foil is included. In addition, a lead piece formed of nickelfor extracting a current was welded to the exposed portion of the copperfoil, and vacuum drying was performed for 12 hours at 80° C., so that alead-attached negative electrode was obtained.

<Assembly of Single-Layered Laminate-Type Battery>

The lead-attached positive electrode and the lead-attached negativeelectrode were overlapped by interposing a polyethylene microporousmembrane separator (having a thickness of 21 μm) while the mixture coatsurfaces of each electrode face each other, so that a laminatedelectrode structure was obtained. This laminated electrode structure washoused in an aluminum laminated sheet package having a size of 90 mm by80 mm, and vacuum drying was performed for 5 hours at 80° C. in order toremove moisture. Subsequently, each of the electrolyte solutionsdescribed above was injected into the package, and the package wassealed, so that a single-layered laminate type (pouch type) non-aqueoussecondary battery (hereinafter, simply referred to as “single-layeredlaminate-type battery”) was manufactured. This single-layeredlaminate-type battery has a design capacity value of 23 mAh and a ratedvoltage value of 4.2 V.

<Evaluation of Single-Layered Laminate-Type Battery>

For the battery for evaluation obtained as described above, initialcharging treatment was performed in the sequence of the followingchapter (1-1). Then, each battery was evaluated in the sequence of thechapters (1-2) and (1-3). Note that the charging/discharging wasperformed using a charging/discharging device ACD-01 (model name)produced by Asuka Electronics Co., Ltd. and a thermostatic oven PLM-63S(model name) produced by Futaba Kagaku Co., Ltd.

Here, “1 C” refers to a current value at which a fully charged batteryis expected to be discharged in one hour at a constant current toterminate the discharge. That is, “1 C” refers to a current value atwhich the discharge operation is expected to be terminated in one hourby discharging the battery from a full-charge state of 4.2 V to avoltage of 3.0 V at a constant current.

(1-1) Initial Charging/Discharging Treatment of Single-LayeredLaminate-Type Battery

The battery was charged with a constant current of 2.3 mA correspondingto “0.1 C” to a voltage of 4.2 V by setting the battery ambienttemperature to 25° C. and was then charged with a constant voltage of4.2 V for 1.5 hours. Then, the battery was discharged with a constantcurrent of 6.9 mA corresponding to “0.3 C” to a voltage of 3.0 V.Initial efficiency was calculated by dividing the discharge capacity atthis time by the charge capacity.

(1-2) 60° C. Full-Charge Storage Test of Single-Layered Laminate-TypeBattery

In the experiment, the single-layered laminate-type battery was chargedwith a constant current of 0.05 C to a voltage of 4.2 V at a temperatureof 25° C. and was then charged with a constant voltage of 4.2 V for 1.5hours. In addition, this charged single-layered laminate-type batterywas stored in the thermostatic oven at a temperature of 60° C. After 720hours, the single-layered laminate-type battery was removed from thethermostatic oven and was recovered to the room temperature.

(1-3) Measurement of Electrochemical Impedance Spectroscopy

The measurement of electrochemical impedance spectroscopy was performedusing a frequency response analyzer 1400 (model name) produced byAMETEK, Inc. and potentio-galvanostat 1470E (model name) produced byAMETEK, Inc. An A.C. impedance value at 1 kHz was obtained as a requiredresistance value by measuring impedance from a voltage/current responsesignal by applying an AC signal while changing the frequency 1000 kHz to0.01 Hz. An amplitude of the applied AC voltage was set to “±5 mV”.Furthermore, the battery ambient temperature at the time of measurementof electrochemical impedance spectroscopy was set to 25° C. In addition,the following values were calculated from such results.Resistance increase rate=(resistance value after 60° C. full-chargestorage test/resistance value before 60° C. full-charge storagetest)×100[%]

As a non-aqueous secondary battery to be measured, a single-layeredlaminate-type battery not subjected to the 60° C. full-charge storagetest and a single-layered laminate-type battery subjected to the 60° C.full-charge storage test were employed using the method described abovein the chapter (1-2). The experimental result is shown in the followingTable 47.

TABLE 47 A.C. impedance value at 1 kHz [Ω] Resistance Before Afterincrease storage storage rate test test [%] Determination Example 1452.5 5.6 224 ∘ Example 146 2.9 6.1 210 ∘ Example 147 3.0 7.0 233 ∘Comparative 3.1 15.2 490 x Example 124 Comparative 3.3 18.1 548 xExample 125 Comparative 3.4 20.1 591 x Example 126

As shown in Table 47, in the examples, it was recognized that theresistance increase rate in the full-charge storage test for 720 hoursat 60° C. is 400% or lower. Preferably, the resistance increase rate is350% or lower, more preferably 300% or lower, and furthermore preferably250% or lower.

It is preferable that a storage battery compatible with a cold region isconfigured by using the non-aqueous secondary battery using theelectrolyte solution containing imide salt contains acetonitrile as thesolvent and LiPO₂F₂ and cyclic acid anhydride as the additives. As aresult, it is possible to suppress an increase of the internalresistance during high-temperature heating and obtain an excellentlow-temperature characteristic.

On the basis of the examples and the comparative examples, it wasrecognized that, if the imide salt is contained in a molarityrelationship of “LiPF₆≤imide salt”, it is possible to suppress reductionof the ionic conductivity at a low temperature and obtain an excellentlow-temperature characteristic. The LiPO₂F₂ and cyclic acid anhydridecontribute to suppression of an increase of the internal resistanceduring high-temperature heating. In addition, it is conceived that theimide salt contributes to improvement of the low-temperaturecharacteristic.

On the basis of the experimental results of Example 145 to 147, it waspreferable that an electrolyte solution containing acetonitrile and atleast one selected from succinic anhydride, maleic anhydride, andphthalic anhydride is employed. As a result, it is possible to suppressan increase of internal resistance during high-temperature heating andobtain an excellent low-temperature characteristic. Therefore, using thenon-aqueous secondary battery containing acetonitrile, it is possible tocope with a storage battery compatible with a cold region.

An example of the specific configuration of the forty fourth embodimentwill now be described. FIGS. 3(a) and (b) are a schematic explanatorydiagram illustrating a cell pack according to the forty fourthembodiment.

In the cell pack (without parallel) of this example illustrated in FIG.3(a), the reference numeral 1 refers to “non-aqueous secondary battery(LIB)”, the reference numeral 2 refers to “voltage monitoring circuit(BMS)”, and the reference numeral 3 refers to “cell pack (withoutparallel)”. The cell pack 3 a can be repeatedly charged and discharged,and a plurality of cell packs 3 a may be connected in parallel.

Specifically, as illustrated in FIG. 3(a), this cell pack 3 a includesnon-aqueous secondary batteries (LIB) 1 in which four cells connected inseries and a voltage monitoring circuit (BMS) 2 that individuallymonitors terminal voltages for each of the plurality of non-aqueoussecondary batteries.

In the cell pack (parallel type) of this example illustrated in FIG.3(b), the reference numeral 1 refers to “non-aqueous secondary battery(LIB)”, the reference numeral 2 refers to “voltage monitoring circuit(BMS)”, and the reference numeral 3 refers to “cell pack (paralleltype)”. The cell pack 3 b can be repeatedly charged and discharged, anda plurality of cell packs 3 b may be connected in parallel.

Specifically, as illustrated in FIG. 3(b), this cell pack 3 b includesfour non-aqueous secondary batteries (LIB) 1 connected in series inwhich a plurality of cells are connected in parallel, and a voltagemonitoring circuit (BMS) 2 that individually monitors terminal voltagesfor each of the plurality of non-aqueous secondary batteries.

Here, in FIGS. 3(a) and 3(b), the non-aqueous secondary battery (LIB) 1includes a positive electrode having a positive-electrode activematerial layer provided on one surface or both surfaces of the currentcollector, and a negative electrode having a negative-electrode activematerial layer provided on one surface or both surface of the currentcollector and the non-aqueous electrolyte solution. If thepositive-electrode active material layer contains iron phosphate lithium(LiFePO₄) including Fe, and the negative-electrode active material layercontains graphite or at least one element selected from a groupconsisting of Ti, V, Sn, Cr, Mn, Fe, Co, Ni, Zn, Al, Si, and B, theoperation voltage range per cell becomes within a range of 1.8 to 3.7 V,and the average operation voltage becomes 2.5 to 3.5 V, so that a 12Vcell pack is obtained. As a result, it is possible to substitute anexisting 12V lead acid battery. Since a specification of an electricsystem is defined on the basis of the operation voltage range of thelead acid battery, it is very important to determine the operationvoltage range per cell. For this reason, the BMS 2 for appropriatelymanaging the voltage is mounted.

In a case where an electrolyte solution containing acetonitrile as amain solvent is used as the lithium ion battery, reductive decompositionproceeds at a negative electrode electric potential of graphite.Therefore, a negative electrode capable of absorbing lithium ions at 0.4V (vs. Li/Li⁺) or higher has been used. However, since the electrolytesolution containing ethylene carbonate or vinylene carbonate and thepositive electrode of iron phosphate lithium (LiFePO₄:LFP) or thenegative electrode of graphite are employed, it is possible to obtain a12V cell pack capable of improving a cycle life at a high temperature.Furthermore, this 12V cell pack has a high input/output characteristicover a wide temperature range.

An example of a specific configuration of the forty fifth embodimentwill now be described. FIG. 4 is a schematic explanatory diagramillustrating a hybrid power system according to the present invention.Here, the reference numeral 1 refers to a “non-aqueous secondary battery(LIB)”, the reference numeral 2 refers to a voltage monitoring circuit(BMS), the reference numeral 4 a refers to a “capacitor (secondarybattery other than the LIB)”, and the reference numeral 5 refers to asmall-sized hybrid power system. This small-sized hybrid power system 5can be repeatedly charged and discharged.

Specifically, as illustrated in FIG. 4, this small-sized hybrid powersystem 5 includes non-aqueous secondary batteries (LIB) 1 in which fourcells are connected in series, and a voltage monitoring circuit (BMS) 2that individually monitors terminal voltages of each of the plurality ofnon-aqueous secondary batteries. In addition, a capacitor 4 a (as asecondary battery other than the LIB) is connected in parallel to theLIB 1. The capacitor preferably includes an electric double layercapacitor, a lithium ion capacitor, or the like.

Here, the non-aqueous secondary battery (LIB) 1 includes a positiveelectrode having a positive-electrode active material layer provided onone surface or both surfaces of the current collector, and a negativeelectrode having a negative-electrode active material layer provided onone surface or both surface of the current collector and the non-aqueouselectrolyte solution. If the positive-electrode active material layercontains iron phosphate lithium (LiFePO₄) including Fe, and thenegative-electrode active material layer contains graphite or at leastone element selected from a group consisting of Ti, V, Sn, Cr, Mn, Fe,Co, Ni, Zn, Al, Si, and B, the operation voltage range per cell becomeswithin a range of 1.8 to 3.7 V, and the average operation voltagebecomes 2.5 to 3.5 V, so that a 12V hybrid power system is obtained. Asa result, it is possible to substitute an existing 12V lead acidbattery. Since a specification of an electric system is defined on thebasis of the operation voltage range of the lead acid battery, it isvery important to determine the operation voltage range per cell. Forthis reason, the BMS for appropriately managing the voltage is mounted.

In a case where an electrolyte solution containing acetonitrile as amain solvent is used as the lithium ion battery, reductive decompositionproceeds at a negative electrode electric potential of graphite.Therefore, a negative electrode capable of absorbing lithium ions at 0.4V (vs. Li/Li⁺) or higher has been used. However, since the electrolytesolution containing ethylene carbonate or vinylene carbonate and thepositive electrode of iron phosphate lithium (LiFePO₄:LFP) and thenegative electrode of graphite are employed, it is possible to obtain a12V hybrid power system capable of improving a cycle life at a hightemperature. Furthermore, this 12V hybrid power system has a highinput/output characteristic over a wide temperature range.

According to the forty fifth embodiment, the hybrid power system is acombinational hybrid power system in which the LIB module of the fortyforth embodiment and the secondary battery other than the lead acidbattery are combined. Here, the module is formed by connecting aplurality of cells, and the cell pack is formed by connecting aplurality of modules. However, the cell pack is a terminology includingthe module. In the LIB of the prior art, an organic solvent is used inthe electrolyte solution. Therefore, viscosity of the electrolytesolution increases at a low temperature, and the internal resistancesignificantly increases. As a result, the low-temperature output powerof the LIB is reduced, compared to the lead acid battery. Meanwhile, thelead acid battery has low output power at 25° C. but has high outputpower at −10° C.

In this regard, according to the forty fifth embodiment, a 12V vehiclepower system is configured by connecting the LIB module of the fortyforth embodiment to the secondary battery other than the lead acidbattery in parallel, and a large current is supplemented to the LIBmodule of the forty forth embodiment capable of receiving a largecurrent in the event of a charge operation caused by braking of vehicledeceleration or the like. As a result, it is possible to efficiently useenergy generated in the event of braking of a traveling vehicle such asan automobile as regenerative energy.

According to the forty fifth embodiment, iron phosphate lithium(LiFePO₄) is used as the positive-electrode active material of the LIB,and graphite is used as the negative-electrode active material, so thatthe electrolyte solution preferably has a 20° C. ionic conductivity of18 mS/cm or higher. Since iron phosphate lithium has lower electronconductivity, compared to NCM or LCO, it has a problem incharging/discharging. For this reason, its advantage may be degradedwhen it is combined with a secondary battery other than the LIB. In thisregard, by using an electrolyte solution having high ionic conductivity,it is possible to cope with a wide temperature range from a lowtemperature to a room temperature in a large-currentcharging/discharging. Therefore, it is possible of extend a servicelife.

An example of the specific configuration of the forty sixth embodimentwill now be described. FIG. 5 is a schematic explanatory diagramillustrating the cell pack according to the forty sixth embodiment.Here, the reference numeral 1 refers to a “non-aqueous secondary battery(LIB)”, the reference numeral 2 refers to a “voltage monitoring circuit(BMS)”, the reference numeral 6 refers to a “module”, and the referencenumeral 7 refers to a “cell pack”. The cell pack 7 can be repeatedlycharged and discharged, and a plurality of cell packs 7 may be connectedin parallel.

This cell pack 7 is configured by connecting, in series, the modules 6formed by connecting one or more cell packs in parallel on the basis ofFormula (3), in which the number of cells in the non-aqueous secondarybattery (LIB) 1 is defined on the basis of the following Formula (2).Note that the non-aqueous secondary battery 1 may be configured byconnecting two or more cells in parallel.Number of cells connected in series per module (X): X=2,4,8, or16  Formula (2)Number of modules connected in series per cell pack (Y): Y=16/X  Formula(3)

Furthermore, the hybrid power system has the connected non-aqueoussecondary batteries (LIB) 1 and a voltage monitoring circuit (BMS) 2that individually monitors terminal voltages of each of the plurality ofnon-aqueous secondary batteries.

Here, the non-aqueous secondary battery (LIB) 1 includes a positiveelectrode having a positive-electrode active material layer provided onone surface or both surfaces of the current collector, and a negativeelectrode having a negative-electrode active material layer provided onone surface or both surface of the current collector and the non-aqueouselectrolyte solution. If the positive-electrode active material layercontains iron phosphate lithium (LiFePO₄) including Fe, and thenegative-electrode active material layer contains graphite or at leastone element selected from a group consisting of Ti, V, Sn, Cr, Mn, Fe,Co, Ni, Zn, Al, Si, and B, the operation voltage range per cell becomeswithin a range of 1.8 to 3.7 V, and the average operation voltagebecomes 2.5 to 3.5 V, so that a 48V cell pack is obtained.

In a case where an electrolyte solution containing acetonitrile as amain solvent is used as the lithium ion battery, reductive decompositionproceeds at a negative electrode electric potential of graphite.Therefore, a negative electrode capable of absorbing lithium ions at 0.4V (vs. Li/Li⁺) or higher has been used. However, since the electrolytesolution containing ethylene carbonate or vinylene carbonate and thepositive electrode of iron phosphate lithium (LiFePO₄:LFP) and thenegative electrode of graphite are employed, it is possible to obtain a48V cell pack capable of improving a cycle life at a high temperature.Furthermore, this 48V cell pack has a high input/output characteristicover a wide temperature range.

An example of the specific configuration of the forty seventh embodimentwill now be described. FIG. 6 is a schematic explanatory diagramillustrating the hybrid power system according to the forty seventhembodiment. Here, the reference numeral 1 refers to a “non-aqueoussecondary battery (LIB)”, the reference numeral 2 refers to a “voltagemonitoring circuit (BMS)”, the reference numeral 4 b refers to a leadacid battery (second battery other than the lead acid battery (LIB)),the reference numeral 6 refers to a “module”, the reference numeral 7refers to a “cell pack”, and the reference numeral 8 refers to a“large-sized hybrid power system”. This large-sized hybrid power system8 can be repeatedly charged and discharged. In addition, a plurality ofcell packs 7 may be connected in parallel.

This cell pack 7 is configured by connecting, in series, the modules 6formed by connecting one or more cell packs in parallel on the basis ofFormula (3), in which the number of cells in the non-aqueous secondarybattery (LIB) 1 is defined on the basis of the following Formula (2).Note that the non-aqueous secondary battery 1 may be configured byconnecting two or more cells in parallel.Number of cells connected in series per module (X): X=2,4,8, or16  Formula (2)Number of modules connected in series per cell pack (Y): Y=16/X  Formula(3)

Furthermore, the hybrid power system has the connected non-aqueoussecondary batteries (LIB) 1 and a voltage monitoring circuit (BMS) 2that individually monitors terminal voltages of each of the plurality ofnon-aqueous secondary batteries.

This large-sized hybrid power system 8 includes lead acid batteries 4 b(secondary batteries other than the LIB) connected to the cell pack 7via a DC/DC converter.

According to the forty seventh embodiment, it is preferable that thepositive-electrode active material of the LIB is iron phosphate lithium(LiFePO₄), the negative-electrode active material of the LIB isgraphite, and the electrolyte solution has an 20° C. ionic conductivityof 15 mS/cm or higher. Since the iron phosphate lithium has a lowerelectron conductivity, compared to NCM or LCO, there may be a problem incharging/discharging, and advantages may be degraded when it is combinedwith the lead acid battery. Therefore, by using the electrolyte solutionhaving a high ionic conductivity, it is possible to cope withlarge-current charging/discharging of the lead acid battery in thevicinity of the room temperature and extend the service life untilreplacement of the battery.

Here, the non-aqueous secondary battery (LIB) 1 includes a positiveelectrode having a positive-electrode active material layer provided onone surface or both surfaces of the current collector, and a negativeelectrode having a negative-electrode active material layer provided onone surface or both surface of the current collector and the non-aqueouselectrolyte solution. If the positive-electrode active material layercontains iron phosphate lithium (LiFePO₄) including Fe, and thenegative-electrode active material layer contains graphite or at leastone element selected from a group consisting of Ti, V, Sn, Cr, Mn, Fe,Co, Ni, Zn, Al, Si, and B, the operation voltage range per cell becomes1.8 to 3.7 V, and the average operation voltage becomes 2.5 to 3.5 V, sothat a 48V hybrid power system is obtained. As a result, it is possibleto easily use the 48V hybrid power system in combination with anexisting 12V lead acid battery. Since a specification of an electricsystem is defined on the basis of the operation voltage range of thelead acid battery, it is very important to determine the operationvoltage range per cell. For this reason, the BMS2 for appropriatelymanaging the voltage is mounted.

In a case where an electrolyte solution containing acetonitrile as amain solvent is used as the lithium ion battery, reductive decompositionproceeds at a negative electrode electric potential of graphite.Therefore, a negative electrode capable of absorbing lithium ions at 0.4V (vs. Li/Li⁺) or higher has been used. However, since the electrolytesolution containing ethylene carbonate or vinylene carbonate and thepositive electrode of iron phosphate lithium (LiFePO₄:LFP) and thenegative electrode of graphite are employed, it is possible to obtain a48V hybrid power system capable of improving a cycle life at a hightemperature. Furthermore, this 48V hybrid power system has a highinput/output characteristic over a wide temperature range.

The non-aqueous secondary battery of the present invention is notparticularly limited. For example, the non-aqueous secondary batteryaccording to the present invention is applicable to a portable devicesuch as a mobile phone, a portable audio device, a personal computer,and an integrated circuit (IC) tag, a rechargeable battery for vehiclessuch as a hybrid vehicle, a plug-in hybrid vehicle, and an electricvehicle, a storage system for home, IT equipment, or the like. Forexample, the non-aqueous secondary battery according to the presentinvention can be preferably applicable to a non-aqueous secondarybattery having a pouch type cell structure. Moreover, when applied to avehicle-mounted rechargeable battery, it is possible to improve thesafety, compared to the prior art.

The non-aqueous secondary battery according to the present invention canbe applicable to cold region applications, outdoor applications insummer, or the like.

This application is based upon Japanese Patent Application Nos.2017-052399, 2017-052256, 2017-052259, 2017-052260, and 2017-052398,filed on Mar. 17, 2017, the entire contents of which are incorporatedherein by reference.

The invention claimed is:
 1. A non-aqueous electrolyte solutioncomprising a non-aqueous solvent, imide salt, Li ions and PF₆ anions,wherein the non-aqueous solvent includes acetonitrile, wherein the PF₆anions are obtained by dissociating LiPF₆, wherein a molar mixing ratioof PF₆ anions relative to the acetonitrile is 0.01 or higher and lowerthan 0.08, wherein the imide salt is contained in a molarityrelationship of LiPF₆≤imide salt, and wherein an activation energy ofthe non-aqueous electrolyte solution in ion conduction is 15 kJ/mol orlower at a temperature of −20 to 0° C.
 2. The non-aqueous electrolytesolution according to claim 1, wherein the activation energy in the ionconduction is 15 kJ/mol or lower at a temperature of 0 to 20° C.
 3. Thenon-aqueous electrolyte solution according to claim 1, furthercomprising at least one lithium salt selected from the group consistingof LiN(SO₂F)₂ and LiPO₂F₂.
 4. The non-aqueous electrolyte solutionaccording to claim 1, further comprising a cyclic acid anhydride.
 5. Thenon-aqueous electrolyte solution according to claim 1, wherein a contentof the imide salt is 0.5 mol or more and 3.0 mol or less with respect toa non-aqueous solvent of 1 L.